In October, I started a challenge to complete the Pokedex in generation 3. I'm currently have around 340 or 350 Pokemon, out of the 386 Pokemon that exist in the first three generations. My challenge was interrupted when I got my Switch for Christmas, as I wanted to play my new games, but I will finish it. Here's how you can complete the Pokedex in generation 3 as well. (Note: This requires multiple games, and I wasn't sure which game to list it under. I went with Emerald just because it seems to be the most popular gen 3 game, but you don't actually need Emerald at all to complete the Pokedex.)

Here is what you will need:

-Two Game Boy Advances
-A GBA link cable
-A Game Cube
-A GBA to Game Cube cable
-Pokemon Ruby
-Pokemon Sapphire
-Pokemon Leaf Green
-Pokemon XD: Gale of Darkness
-Pokemon Colosseum
-Pokemon Colosseum Bonus Disc if you want Jirachi (US)
-A lot of time, patience, and dedication

If you have Pokemon Emerald and you want to use it you can, but you still need either Ruby or Sapphire as well. If you use Ruby and Emerald you can't get Lunatone and if you use Sapphire and Emerald you can't get Zangoose, however both Lunatone and Zangoose can be acquired in Pokemon XD. Pokemon Emerald also gives you access to a lot of Johto Pokemon, however you will be required to snag and purify these Pokemon in Colosseum anyway to get Ho-Oh (I'll discuss how to get Ho-Oh later).

Also, the reason you need Leaf Green rather than Fire Red, is that all of the version exclusive Pokemon from Fire Red can be obtained through other means. However, the only way to acquire the Slowpoke line is through Leaf Green. You can use Fire Red in addition to Leaf Green if you wish, but it won't help much, since there are no Pokemon that are unique to Fire Red.

I am now going to list every Pokemon and the possible ways to obtain them in generation 3. After that I will discuss what I consider to be the best and easiest way to catch em all.

Bulbasaur - Fire Red or Leaf Green; starter Pokemon

Ivysaur - Evolve Bulbasaur

Venusar - Evolve Ivysaur

Charmander - Fire Red or Leaf Green; starter Pokemon

Charmeleon - Evolve Charmander

Charizard - Evolve Charmeleon

Squirtle - Fire Red or Leaf Green; starter Pokemon

Wartortle - Evolve Squirtle

Blastoise - Evolve Wartortle

Caterpie - Fire Red or Leaf Green; Viridian Forest, Route 24, Route 25 Six Island Pattern Bush
Metapod - Evolve Caterpie / Fire Red or Leaf Green; Viridian Forest, Route 24, Route 25, Six Island Pattern Bush

Butterfree - Evolve Metapod / XD; Cipher Key Lair

Weedle - Fire Red or Leaf Green; Viridian Forest, Route 24, Route 25, Six Island Pattern Bush

Kakuna - Evolve Weedle / Fire Red or Leaf Green; Viridian Forest, Route 24, Route 25, Six Island Pattern Bush

Beedrill - Evolve Kakuna / XD; Cipher Key Lair

Pidgey - Fire Red or Leaf Green; Routes 1, 2, 3, 5, 6, 7, 8, 12, 13, 14, 15, 24, and 25, Bond Bridge, Berry Forest, Five Isle Meadow

Pidgeotto - Evolve Pidgey / Fire Red or Leaf Green; Route 13, Route 14, Route 15, Bond Bridge, Berry Forest, Five Isle Meadow

Pidgeot - Evolve Pidgeotto

Rattata - Fire Red or Leaf Green; Routes 1, 2, 4, 9, 16, 17, 18, and 22, Pokemon Mansion

Raticate - Evolve Rattata / Fire Red or Leaf Green; Route 16, Route 17, Route 18, Pokemon Mansion / XD; Citadark Isle

Spearow - Fire Red or Leaf Green; Routes 3, 4, 9, 10, 11, 16, 17, 18, 22, and 23, Treasure Beach, Mt. Ember, Cape Brink, Ruin Valley, Water Path, Canyon Entrance, Kindle Road / XD; Phenac City

Fearow - Evolve Spearow / Fire Red or Leaf Green; Routes 17, Route 18, Route 23, Treasure Beach, Kindle Road, Mt. Ember, Cape Brink, Ruin Valley, Water Path, Canyon Entrance, Sevault Canyon

Ekans - Breed Arbok / Fire Red; Routes 4, 8, 9, 10, 11, and 23

Arbok - Evolve Ekans / Fire Red; Route 23, Victory Road / XD; Cipher Key Lair

Pikachu - Ruby, Sapphire, or Emerald; Safari Zone / Fire Red or Leaf Green; Viridian Forest, Power Plant

Raichu - Evolve Pikachu

Sandshrew - Ruby or Sapphire; Route 111, Route 113 / Emerald; Route 111 or Mirage Tower / Leaf Green; Routes 4, 8, 9, 10, 11, and 23 / XD; Rock Poke Spot

Sandslash - Evolve Sandshrew / Leaf Green; Route 23, Victory Road

Nidoran (F) - Fire Red or Leaf Green; Route 3, Safari Zone (Also available via in-game trade in Fire Red)

Nidorina - Evolve Nidoran (F) / Fire Red or Leaf Green; Safari Zone (Also available via in-game trade in Fire Red)

Nidoqueen - Evolve Nidorina

Nidoran (M) - Fire Red or Leaf Green; Route 3, Safari Zone (Also available via in-game trade in Leaf Green)

Nidorino - Evolve Nidoran (M) / Fire Red or Leaf Green; Safari Zone (Also available via in-game trade in Leaf Green)

Nidoking - Evolve Nidorino

Clefairy - Fire Red or Leaf Green; Mt. Moon, Rocket Game Corner

Clefable - Evolve Clefairy

Vulpix - Leaf Green; Route 7, Route 8, Pokemon Mansion / XD; ONBS

Ninetales - Evolve Vulpix

Jigglypuff - Ruby, Sapphire, or Emerald; Route 115 / Fire Red or Leaf Green; Route 3

Wigglytuff - Evolve Jigglypuff

Zubat - Ruby, Sapphire, or Emerald; Cave of Origin, Granite Cave, Victory Road, Meteor Falls, Seafloor Cavern, Shoal Cave / Fire Red or Leaf Green; Mt. Moon, Rock Tunnel, Seafoam Islands, Victory Road, Icefall Cave, Lost Cave, Altering Cave / XD; Cave Poke Spot

Golbat - Ruby, Sapphire, or Emerald; Cave of Origin, Shoal Cave, Sky Pillar, Meteor Falls, Seafloor Cavern, Victory Road / Fire Red or Leaf Green; Cerulean Cave, Icefall Cave, Lost Cave, Seafoam Islands, Victory Road

Oddish - Ruby, Sapphire, or Emerald; Routes 110, 117, 119, 120, 121, and 123, Safari Zone / Fire Red; Routes 5, 6, 7, 12, 13, 14, 15, 24, and 25, Berry Forest, Bond Bridge, Cape Brink, Water Path

Gloom - Evolve Oddish / Ruby, Sapphire, or Emerald; Route 121, Route 123, Safari Zone / Fire Red; Routes 12, 13, 14, and 15, Berry Forest, Bond Bridge, Cape Brink, Water Path

Vileplume - Evolve Gloom

Paras - Fire Red or Leaf Green; Mt. Moon, Safari Zone / XD; Cipher Key Lair

Parasect - Evolve Paras / Fire Red or Leaf Green; Safari Zone, Cerulean Cave

Venonat - Fire Red or Leaf Green; Routes 12, 13, 14, and 15, Berry Forest, Bond Bridge, Safari Zone

Venomoth - Evolve Venonat / Fire Red or Leaf Green; Safari Zone, Berry Forest / XD; Cipher Key Lair

Diglett - Fire Red or Leaf Green; Diglett's Cave

Dugtrio - Evolve Diglett / Fire Red or Leaf Green; Diglett's Cave / XD; Citadark Isle

Meowth - Emerald; In-game trade at Battle Frontier / Fire Red or Leaf Green; Routes 5, 6, 7, and 8, Bond Bridge, Canyon Entrance, Cape Brink, Five Isle Meadow, Kindle Road, Ruin Valley, Sevault Canyon, Treasure Beach, Water Path / XD; Phenac City

Persian - Evolve Meowth / Fire Red or Leaf Green; Bond Bridge, Canyon Entrance, Cape Brink, Five Isle Meadow, Kindle Road, Ruin Valley, Sevault Canyon, Treasure Beach, Water Path

Psyduck - Ruby, Sapphire, or Emerald - Safari Zone / Fire Red; Routes 4, 6, 10, 11, 12, 13, 19, 20, 21, 22, 23, 24, and 25, Water Labyrinth, Resort Gorgeous, Memorial Pillar, Green Path, Outcast Island, Tanoby Ruins, Pallet Town, Cerulean City, Vermilion City, Celadon City, Cinnabar Island, One Island, Five Island, Trainer Tower, Viridian City, Fuchsia City, Four Island, Cerulean Cave, Safari Zone, Treasure Beach, Kindle Road, Bond Bridge, Five Isle Meadow, Ruin Valley, Water Path, Cape Brink, Berry Forest, Seafoam Islands, Icefall Cave

Golduck - Evolve Psyduck / Ruby, Sapphire, and Emerald; Safari Zone / Fire Red; Cerulean Cave, Seafoam Islands, Berry Forest, Cape Brink / XD; Citadark Isle

Mankey - Fire Red or Leaf Green; Routes 3, 4, 22, and 23, Rock Tunnel

Primeape - Evolve Mankey / Fire Red or Leaf Green; Route 23, Cerulean Cave, Victory Road / XD; Ciper Key Lair

Growlite - Fire Red; Route 7, Route 8, Pokemon Mansion / XD; Cipher Key Lair

Arcanine - Evolve Growlithe

Poliwag - Fire Red or Leaf Green; Routes 6, 22, 23, and 25, Four Island, Viridian City, Cape Brink, Cerulean Cave, Icefall Cave, Ruin Valley, Fuchsia City, Berry Forest, Safari Zone

Poliwhirl - Evolve Poliwag / Routes 6, 22, 23, and 25, Four Island, Viridian City, Cape Brink, Cerulean Cave, Icefall Cave, Ruin Valley

Poliwrath - Evolve Poliwhirl / XD; Citadark Isle

Abra - Ruby, Sapphire, or Emerald; Granite Cave (Also available in Route 116 in Emerald) / Fire Red or Leaf Green; Route 24, Route 25, Rocket Game Corner

Kadabra - Evolve Abra / Fire Red or Leaf Green; Cerulean Cave

Alakazam - Evolve Kadabra

Machop - Ruby, Sapphire, or Emerald; Fiery Path, Jagged Pass (Also available in Route 112 in Ruby or Sapphire) / Fire Red or Leaf Green; Mt. Ember, Rock Tunnel, Victory Road

Machoke - Evolve Machop / Fire Red or Leaf Green; Cerulean Cave, Mt. Ember, Victory Road

Machamp - Evolve Machoke

Bellsprout - Breed Weepinbell / Leaf Green; Routes 5, 6, 7, 12, 13, 14, 15, 24, and 25, Berry Forest, Bond Bridge, Cape Brink, Water Path

Weepinbell - Evolve Bellsprout / Leaf Green; Routes 12, 13, 14, and 15, Berry Forest, Bond Bridge, Cape Brink, Water Path / XD; Cipher Key Lair

Victreebel - Evolve Weepinbell

Tentacool - Ruby, Sapphire, or Emerald; Routes 103, 105, 106, 107, 108, 109, 110, 115, 118, 119, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, and 134, Slateport City, Pacifidlog Town, Mossdeep City, Lilycove City, Dewford Town, Shoal Cave, Seafloor Cavern, Ever Grande City, Sootopolis City, Abandoned Ship / Fire Red or Leaf Green; Routes 4, 10, 11, 12, 13, 19, 20, 21, and 24, Treasure Beach, Kindle Road, Bond Bridge, Five Isle Meadow, Memorial Pillar, Water Labyrinth, Resort Gorgeous, Water Path, Green Path, Outcast Island, Tanoby Ruins, Pallet Town, Cerulean City, Vermilion City, One Island, Five Island, Icefall Cave, Trainer Tower, Cinnabar Island

Tentacruel - Evolve Tentacool / Ruby, Sapphire, or Emerald; Abandoned Ship / Fire Red or Leaf Green; Treasure Beach, Kindle Road, Bond Bridge, Five Isle Meadow, Memorial Pillar, Water Labyrinth, Resort Gorgeous, Water Path, Green Path, Outcast Island, Tanoby Ruins, One Island, Five Island, Icefall Cave, Trainer Tower

Geodude - Ruby, Sapphire, or Emerald; Granite Cave, Rock Smash (Also available in Magma Hideout in Emerald) / Fire Red or Leaf Green; Victory Road, Mt. Moon, Kindle Road, Rock Tunnel, Mt. Ember

Graveler - Evolve Geodude / Ruby, Sapphire, or Emerald; Rock Smash in Victory Road (Also available in Magma Hideout in Emerald) / Fire Red or Leaf Green; Rock Smash

Golem - Evolve Graveler

Ponyta - Fire Red or Leaf Green; Kindle Road or Mt. Ember

Rapidash - Evolve Ponyta / Fire Red or Leaf Green; Kindle Road or Mt. Ember / XD; Citadark Isle

Slowpoke - Leaf Green; Routes 4, 6, 10, 11, 12, 13, 19, 20, 21, 22, 23, 24, 25, Water Labyrinth, Resort Gorgeous, Memorial Pillar, Green Path, Outcast Island, Tanoby Ruins, Pallet Town, Cerulean City, Vermilion City, Celadon City, Cinnabar Island, One Island, Five Island, Trainer Tower, Viridian City, Fuchsia City, Four Island, Cerulean Cave, Safari Zone, Treasure Beach, Kindle Road, Bond Bridge, Five Isle Meadow, Ruin Valley, Water Path, Cape Brink, Berry Forest, Seafoam Islands, Icefall Cave, Canyon Entrance

Slowbro - Evolve Slowpoke / Leaf Green; Cerulean Cave, Berry Forest, Seafoam Islands, Cape Brink, Cinnabar Island

Magnemite - Ruby, Sapphire, or Emerald; New Mauville / Fire Red or Leaf Green; Power Plant

Magneton - Evolve Magnemite / Ruby, Sapphire or Emerald; New Mauville / Fire Red of Leaf Green; Power Plant, Cerulean Cave / XD; Cipher Key Lair

Farfetch'd - Fire Red or Leaf Green; In-game trade in Vermilion City / XD; Citadark Isle

Doduo - Ruby, Sapphire, or Emerald; Safari Zone / Fire Red or Leaf Green; Route 16, Route 17, Route 18, Safari Zone

Dodrio - Evolve Doduo / Ruby, Sapphire, or Emerald; Safari Zone / XD; Citadark Isle

Seel - Fire Red or Leaf Green; Seafoam Islands, Icefall Cave, In-game trade at Pokemon Lab / XD; Phenac City

Dewgong - Evolve Seel / Fire Red or Leaf Green; Seafoam Islands, Icefall Cave

Grimer - Ruby, Sapphire, or Emerald; Fiery Path / Fire Red or Leaf Green; Pokemon Mansion, Celadon City / XD; Phenac City

Muk - Evolve Grimer / Leaf Green; Pokemon Mansion

Shellder - Fire Red; Pallet Town, Cinnabar Island, Vermilion City, One Island, Five Island, Icefall Cave / XD; Cipher Key Lair

Cloyster - Evolve Shellder

Gastly - Fire Red or Leaf Green; Pokemon Tower, Lost Cave

Haunter - Evolve Gastly / Fire Red or Leaf Green; Pokemon Tower, Lost Cave

Gengar - Evolve Haunter

Onix - Fire Red or Leaf Green; Rock Tunnel, Victory Road, Sevault Canyon

Drowzee - Fire Red or Leaf Green; Route 11, Berry Forest

Hypno - Evolve Drowzee / Fire Red or Leaf Green; Berry Forest / XD; Cipher Key Lair

Krabby - Fire Red or Leaf Green; Routes 4, 10, 11, 12, 13, 19, 20, 21, and 24, Cerulean City, Vermilion City, Seafoam Islands, Cinnabar Island, Pallet Town (Also available in Treasure Beach, Kindle Road, Bond Bridge, Resort Gorgeous, Water Labyrinth, Water Path, Green Path, Outcast Island, Tanoby Ruins, Five Isle Meadow, Memorial Pillar, One Island, Five Island, Icefall Cave, Trainer Tower in Leaf Green)

Kingler - Evolve Krabby / Leaf Green; Route 19, Route 20, Route 21, Kindle Road, Treasure Beach, Bond Bridge, Resort Gorgeous, Water Labyrinth, Five Isle Meadow, Memorial Pillar, Green Path, Water Path, Outcast Island, Trainer Tower, Tanoby Ruins, One Island, Five Island, Icefall Cave, Pallet Town

Voltorb - Ruby, Sapphire, or Emerald; New Mauville / Fire Red or Leaf Green; Route 10, Power Plant / XD; Cave Poke Spot

Electrode - Evolve Voltorb / Ruby, Sapphire, or Emerald; New Mauville, Team Aqua (Magma in Ruby) Hideout / Fire Red or Leaf Green; Power Plant, Cerulean Cave, In-game trade in Pokemon Lab

Exeggcute - Fire Red or Leaf Green; Safari Zone, Berry Forest

Exeggutor - Evolve Exeggcute / XD; Citadark Isle

Cubone - Fire Red or Leaf Green; Pokemon Tower, Sevault Canyon

Marowak - Evolve Cubone / Fire Red or Leaf Green; Victory Road, Sevault Canyon / XD; Citadark Isle

Hitmonlee - Evolve Tyrogue / Fire Red or Leaf Green; Fighting Dojo / XD; Citadark Isle

Hitmonchan - Evolve Tyrogue / Fire Red or Leaf Green; Fighting Dojo / XD; Citadark Isle

Lickitung - Fire Red or Leaf Green; In-game trade on Route 18 / XD; Citadark Isle
Koffing - Ruby, Sapphire, or Emerald; Fiery Path / Fire Red or Leaf Green; Pokemon Mansion, Celadon City

Weezing - Evolve Koffing / Fire Red; Pokemon Mansion

Rhyhorn - Ruby, Sapphire, or Emerald; Safari Zone / Fire Red or Leaf Green; Safari Zone

Rhydon - Evolve Rhyhorn / XD; Citadark Isle

Chansey - Fire Red or Leaf Green; Safari Zone / XD; Citadark Isle

Tangela - Fire Red or Leaf Green; Route 21, Treasure Beach, In-game trade in Pokemon Lab / XD; Cipher Key Lair

Kangaskhan - Fire Red or Leaf Green; Safari Zone / XD; Citadark Isle

Horsea - Ruby, Sapphire, or Emerald; Route 132, Route 133, Route 134 (Also available via in-game trade in Pacifidlog Town in Emerald) / Fire Red or Leaf Green; Routes 4, 10, 11, 12, 13, 19, 20, 21, and 24, Cerulean City, Seafoam Islands, Pallet Town, Cinnabar Island, Vermilion City (Also available in Treasure Beach, Kindle Road, Bond Bridge, Resort Gorgeous, Water Labyrinth, Water Path, Green Path, Outcast Island, Tanoby Ruins, Five Isle Meadow, Memorial Pillar, One Island, Five Island, Icefall Cave, Trainer Tower in Fire Red)

Seadra - Evolve Horsea / Fire Red; Route 19, Route 20, Route 21, Kindle Road, Treasure Beach, Bond Bridge, Resort Gorgeous, Water Labyrinth, Five Isle Meadow, Memorial Pillar, Green Path, Water Path, Outcast Island, Trainer Tower, Tanoby Ruins, Cinnabar Island, One Island, Five Island, Icefall Cave, Pallet Town

Goldeen - Ruby, Sapphire, or Emerald; Routes 102, 111, 114, 117, and 120, Petalburg City, Meteor Falls, Victory Road, Safari Zone / Fire Red or Leaf Green; Routes 6, 22, 23, 25, Ruin Valley, Cape Brink, Viridian City, Four Island, Cerulean Cave, Icefall Cave, Fuchsia City, Berry Forest, Safari Zone

Seaking - Evolve Goldeen / Ruby, Sapphire, or Emerald; Safari Zone / Fire Red or Leaf Green; Berry Forest, Safari Zone, Fuchsia City

Staryu - Ruby, Sapphire, or Emerald; Lilycove City / Leaf Green; Pallet Town, Vermilion City, Cinnabar Island, One Island, Five Island, Icefall Cave

Starmie - Evolve Staryu / XD; Citadark Isle

Mr. Mime - Fire Red or Leaf Gren; In-game trade on Route 2 / XD; Citadark Isle

Scyther - Fire Red; Safari Zone, Rocket Game Corner / XD; Citadark Isle

Jynx - Fire Red or Leaf Green; In-Game trade in Cerulean City

Electabuzz - Fire Red; Power Plant / XD; Citadark Isle

Magmar - Leaf Green; Mt. Ember / XD; Citadark Isle

Pinsir - Ruby, Sapphire, or Emerald; Safari Zone / Leaf Green; Safari Zone, Rocket Game Corner / XD; Citadark Isle

Tauros - Fire Red or Leaf Green; Safari Zone / XD; Citadark Isle

Magikarp - Ruby, Sapphire, or Emerald; Routes 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 114, 115, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, and 134, Petalburg City, Dewford Town, Slateport City, Lilycove City, Pacifidlog Town, Ever Grande City, Abandoned Ship, Safari Zone, Shoal Cave, Meteor Falls, Seafloor Cavern, Victory Road, Mossdeep City, Safari Zone, Sootopolis City / Fire Red or Leaf Green; Routes 4, 6, 10, 11, 12, 13, 19, 20, 21, 22, 23, 24, and 25, Treasure Beach, Kindle Road, Cape Brink, Bond Bridge, Five Isle Meadow, Ruin Valley, Water Path, Water Labyrinth, Resort Gorgeous, Memorial Pillar, Green Path, Outcast Island, Tanoby Ruins, Pallet Town, Cerulean City, Viridian City, Fuchsia City, Vermilion City, Celadon City, Cinnabar Island, One Island, Four Island, Five Island, Trainer Tower, Cerulean Cave, Safari Zone, Berry Forest, Icefall Cave, Seafoam Island, Magikarp salesman on Route 4

Gyarados - Evolve Magikarp / Ruby, Sapphire, or Emerald; Sootopolis City / Fire Red or Leaf Green; Routes 4, 6, 10, 11, 12, 13, 19, 20, 21, 22, 23, 24, and 25, Treasure Beach, Kindle Road, Cape Brink, Bond Bridge, Five Isle Meadow, Ruin Valley, Water Path, Water Labyrinth, Resort Gorgeous, Memorial Pillar, Green Path, Outcast Island, Tanoby Ruins, Pallet Town, Cerulean City, Viridian City, Fuchsia City, Vermilion City, Cinnabar Island, One Island, Four Island, Five Island, Seafoam Islands, Trainer Tower, Cerulean Cave, Berry Forest, Icefall Cave

Lapras - Fire Red or Leaf Green; Gift Pokemon in Silph Co, Icefall Cave / XD; Citadark Isle

Ditto - Emerald; Desert Underpass / Fire Red or Lead Green; Route 13, Route 14, Route 15, Pokemon Mansion, Cerulean Cave

Eevee - Fire Red or Leaf Green; Gift Pokemon in Pokemon Mansion / XD; Starter Pokemon

Vaporon - Evolve Eevee

Jolteon - Evolve Eevee

Flareon - Evolve Eevee

Porygon - Fire Red or Leaf Green; Rocket Game Corner

Omanyte - Fire Red or Leaf Green; Revive Helix Fossil from Mt. Moon at Pokemon Lab

Omastar - Evolve Omanyte

Kabuto - Fire Red or Leaf Green; Revive Dome Fossil from Mt. Moon at Pokemon Lab

Kabutops - Evolve Kabuto

Aerodactyl - Fire Red or Leaf Green; Revive Old Amber from Pewter Museum at Pokemon Lab

Snorlax - Fire Red or Leaf Green; Route 12, Route 16 / XD; Citadark Isle

Articuno - Fire Red or Leaf Green; Seafoam Islands / XD; Citadark Isle

Zapdos - Fire Red or Leaf Green; Power Plant / XD; Citadark Isle

Moltres - Fire Red or Leaf Green; Mt. Ember / XD; Citadark Isle

Dratini - Breed Dragonite / Fire Red or Leaf Green; Safari Zone, Rocket Game Corner

Dragonair - Evolve Dratini / Fire Red or Leaf Green; Safari Zone

Dragonite - Evolve Dragonair / XD; Gateon Port

Mewtwo - Fire Red or Leaf Green; Cerulean Cave

Mew - Impossible to obtain, unless you attended a Pokemon Emerald event in 2005 in Japan. Completely impossible to obtain in North America.

Chikorita - Breed Bayleef or Meganium / Emerald; One of three Pokemon that can be chosen for completing the Hoenn Dex / XD; One of three Pokemon that can be chosen for defeating 100 trainers at Mt. Battle

Bayleef - Evolve Chikorita / Colosseum; Phenac City

Megnium - Evolve Bayleef

Cyndaquil - Breed Quilava or Typhlosion / Emerald; One of three Pokemon that can be chosen for completing the Hoenn Dex / XD; One of three Pokemon that can be chosen for defeating 100 trainers at Mt. Battle

Quilava - Evolve Cyndaquil / Colosseum; Phenac City

Typhlosion - Evolve Quilava

Totodile - Breed Croconaw or Feraligatr / Emerald; One of three Pokemon that can be chosen for completing the Hoenn Dex / XD; One of three Pokemon that can be chosen for defeating 100 trainers at Mt. Battle

Croconaw - Evolve Totodile / Colosseum; Phenac City

Feraligatr - Evolve Croconaw

Sentret - Fire Red or Leaf Green; Canyon Entrance, Five Isle Meadow, Water Path

Furret - Evolve Sentret / Colosseum; Pyrite Town

Hoothoot - Breed Noctowl / Emerald; Safari Zone

Noctowl - Evolve Hoothoot / Colosseum; Pyrite Town

Ledyba - Breed Ledian / Emerald; Safari Zone / Fire Red or Leaf Green; Pattern Bush / XD; Gateon Port

Ledian - Evolve Ledyba / Colosseum; The Under

Spinarak - Breed Ariados / Emerald; Safari Zone / Fire Red or Leaf Green; Pattern Bush / XD; Cipher Lab

Ariados - Evolve Spinarak / Colosseum; Shadow Pokemon Lab

Crobat - Evolve Golbat

Chinchou - Ruby, Sapphire, or Emerald; Underwater

Lanturn - Evolve Chinchou

Pichu - Breed Pikachu or Raichu

Cleffa - Breed Clefairy or Clefable

Igglybuff - Breed Jigglypuff or Wigglytuff

Toegpi - Fire Red or Leaf Green; Hatch egg from man in Water Labyrinth / XD; Received from Hordel

Togetic - Evolve Togepi / Colosseum; Outskirt Stand

Natu - Ruby, Sapphire or Emerald; Safari Zone / Fire Red or Leaf Green; Ruin Valley / XD; Phenac City

Xatu - Evolve Natu / Ruby, Sapphire, or Emerald; Safari Zone

Mareep - Breed Flaaffy or Ampharos / Emerald; Safari Zone / XD; Cipher Lab

Flaaffy - Evolve Mareep / Colosseum; Pyrite Town

Ampahros - Evolve Flaaffy

Bellossom - Evolve Gloom

Marill - Ruby, Sapphire, or Emerald; Routes 102, 111, 114, 117, and 120, Petalburg City (Also available in Route 104, Route 112, Safari Zone in Emerald) / Leaf Green; Four Island, Icefall Cave, Ruin Valley

Azumarill - Evolve Marill

Sudowoodo - Emerald; Battle Frontier / Colosseum; Pyrite Cave

Politoed - Evolve Poliwhirl

Hoppip - Fire Red or Leaf Green; Five Island, Resort Gorgeous, Water Labyrinth, Five Isle Meadow, Memorial Pillar / XD; Oasis Poke Spot

Skiploom - Evolve Hoppip / Colosseum; Pyrite Town

Jumpluff - Evolve Skiploom

Aipom - Emerald; Safari Zone / Colosseum; Shadow Pokemon Lab

Sunkern - Breed Sunflora / Emerald; Safari Zone

Sunflora - Evolve Sunkern / Colosseum; Realgam Tower

Yanma - Fire Red or Leaf Green; Ruin Valley / Colosseum; Pyrite Building

Wooper - Breed Quagsire / Emerald; Safari Zone / Fire Red; Four Island, Icefall Cave, Ruin Valley / XD; Cave Poke Spot

Quagsire - Evolve Wooper / Emerald; Safari Zone / Colosseum; Pyrite Town

Espeon - Evolve Eevee (in Ruby, Sapphire, Emerald if battery hasn't run dry or in XD) / Colosseum; Starter Pokemon

Umbreon - Evolve Eevee (in Ruby, Sapphire, Emerald if battery hasn't run dry or in XD) / Colosseum; Starter Pokemon

Murkrow - Fire Red; Lost Cave / Colosseum; Shadow Pokemon Lab

Slowking - Evolve Slowpoke

Misdreavus - Leaf Green; Lost Cave / Colosseum; Pyrite Town

Unown - Fire Red or Leaf Green; Tanoby Chambers

Wobbuffet - Evolve Wynaut / Ruby, Sapphire, or Emerald; Safari Zone / Fire Red or Leaf Green; Cerulean Cave, Ruin Valley

Girafarig - Ruby, Sapphire, or Emerald; Safari Zone

Pineco - Breed Forretress / Emerald; Safari Zone / XD; Phenac City

Forretress - Evolve Pineco / Colosseum; Shadow Pokemon Lab

Dunsparce - Fire Red or Leaf Green; Three Isle Port / Colosseum; Pyrite Cave

Gligar - Emerald; Safari Zone / Colosseum; The Under Subway / XD; Rock Poke Spot

Steelix - Evolve Onix

Snubbull - Breed Granbull / Emerald; Safari Zone

Granbull - Evolve Snubbull / Colosseum; Shadow Pokemon Lab

Qwilfish - Fire Red; Five Isle Meadow, Green Path, Memorial Pillar, Outcast Island, Resort Gorgeous, Tanoby Ruins, Trainer Tower, Water Labyrinth, Water Path / Colosseum; Pyrite Town

Scizor - Evolve Scyther

Shuckle - Emerald; Safari Zone / Colosseum; Deep Colosseum / XD; In-game trade in Pyrite Town

Heracross - Ruby, Sapphire, or Emerald; Safari Zone / Fire Red or Leaf Green; Pattern Bush / Colosseum; Realgam Tower

Sneasel - Leaf Green; Icefall Cave / Colosseum; The Under Subway

Teddiursa - Breed Ursaring / Emerald; Safari Zone / XD; Pokemon HQ Lab

Ursaring - Evolve Teddiursa / Colosseum; Snagem Hideout

Slugma - Breed Magcargo / Ruby, Sapphire, or Emerald; Fiery Path (Also available in Route 113 in Emerald) / Fire Red or Leaf Green; Mt. Ember / Colosseum; Pyrite Town

Magcargo - Evolve Slugma / Fire Red or Leaf Green; Mt. Ember / XD; Citadark Isle

Swinub - Breed Piloswine / Fire Red or Leaf Green; Icefall Cave / XD; Phenac City

Piloswine - Evolve Swinub / Colosseum; The Under Subway

Corsola - Ruby, Sapphire, or Emerald; Route 128, Ever Grande City (Also available via in-game trade in Pacifidlog Town in Ruby or Sapphire)

Remoraid - Emerald; Safari Zone / Leaf Green; Five Isle Meadow, Green Path, Memorial Pillar, Outcast Island, Resort Gorgeous, Tanoby Ruins, Trainer Tower, Water Labyrinth, Water Path / Colosseum; Pyrite Town

Octillery - Evolve Remoraid / Emerald; Safari Zone

Delibird - Fire Red; Icefall Cave / Colosseum; Realgam Tower

Mantine - Leaf Green; Tanoby Ruins, Trainer Tower / Colosseum; Pyrite Town

Skarmory - Ruby, Sapphire, or Emerald; Route 113 / Fire Red; Sevault Canyon / Colosseum; Realgam Tower

Houndour - Breed Houndoom / Emerald; Safari Zone / XD; Cipher Lab

Houndoom - Evolve Houndour / Colosseum; Tower Colosseum

Kingdra - Evolve Seadra

Phanpy - Ruby, Sapphire, or Emerald; Safari Zone / Fire Red or Leaf Green; Sevault Canyon, Canyon Entrance / XD; Oasis Poke Spot

Donphan - Evolve Phanpy

Porygon2 - Evolve Porygon

Stantler - Emerald; Safari Zone / Colosseum; The Under Subway

Smeargle - Emerald; Artisan Cave / Colosseum; Snagem Hideout

Tyrogue - Breed Hitmonlee, Hitmonchan, or Hitmontop

Hitmontop - Evolve Tyrogue / Colosseum; Agate Village

Smoochum - Breed Jynx

Elekid - Breed Electabuzz

Magby - Breed Magmar

Miltank - Emerald; Safari Zone / Colosseum; Tower Colosseum

Blissey - Evolve Chansey

Raikou - Fire Red or Leaf Green; Roaming if you chose Squirtle / Colosseum; Shadow Pokemon Lab

Entei - Fire Red or Leaf Green; Roaming if you chose Bulbasaur / Colosseum; Mt. Battle

Suicune - Fire Red or Leaf Green; Roaming if you chose Charmander / Colosseum; The Under

Larvitar - Breed Tyranitar / Fire Red or Leaf Green; Sevault Canyon / XD; In-game trade in Pyrite Town

Pupitar - Evolve Larvitar

Tyranitar - Evolve Pupitar / Colosseum; Tower Colosseum

Luiga - XD; Citadark Isle

Ho-Oh - Colosseum; Mt. Battle

Celebi - Colosseum; Purify all shadow Pokemon, and have Japanese bonus disc. Impossible to obtain in North America.

Treecko - Ruby, Sapphire, or Emerald; Starter Pokemon

Grovyle - Evolve Treecko

Sceptile - Evolve Grovyle

Torchic - Ruby, Sapphire, or Emerald; Starter Pokemon

Combusken - Evolve Torchic

Blaziken - Evolve Combusken

Mudkip - Ruby, Sapphire, or Emerald; Starter Pokemon

Marshtomp - Evolve Mudkip

Swampert - Evolve Marshtomp

Poochyena - Ruby, Sapphire, or Emerald; Route 101, Route 102, Route 103 (Also available in Routes 104, 110, 116, 117, 120, 121, and 123, Petalburg Woods in Emerald)

Mightyena - Evolve Poochyena / Emerald; Route 120, Route 121, Route 123

Zigzagoon - Ruby, Sapphire, or Emerald; Routes 101, 102, 103, 118, and 119 (Also availabe in Routes 104, 110, 116, 117, 120, 121, and 123, Petalburg Woods in Ruby or Sapphire)

Linoone - Evolve Zigzagoon / Ruby, Sapphire, or Emerald; Route 118, Route 119 (Also available in Route 120, Route 121, Route 123 in Ruby or Sapphire)

Wurmple - Ruby, Sapphire, or Emerald; Route 101, Route 102, Route 104, Petalburg Woods

Silcoon - Evolve Wurmple / Ruby, Sapphire or Emerald; Petalburg Woods

Beautifly - Evolve Silcoon

Cascoon - Evolve Wurmple / Ruby, Sapphire or Emerald; Petalburg Woods

Dustox - Evolve Cascoon

Lotad - Sapphire or Emerald; Route 102, Route 114

Lombre - Evolve Lotad / Sapphire or Emerald; Route 114

Ludicolo - Evolve Lombre

Seedot - Ruby or Sapphire; Route 102 (Also availabe in Route 114 in Ruby / Route 117, Route 120, via in-game trade in Rustboro City in Emerald) / XD; Cipher Lab

Nuzleaf - Evolve Seedot / Ruby or Emerald; Route 114

Shiftry - Evolve Nuzleaf

Taillow - Breed Swellow / Ruby, Sapphire, or Emerald; Route 104, Route 115, Route 116, Petalburg Woods

Swellow - Evolve Taillow / Ruby, Sapphire, or Emerald; Route 115 / XD; Citadark Isle

Wingull - Ruby, Sapphire, or Emerald; Routes 103, 104, 105, 106, 107, 108, 109, 110, 115, 118, 119, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, and 134, Dewford Town, Ever Grande City, Lilycove City, Mossdeep City, Pacifidlog Town, Slateport City, outside Mt. Pyre

Pelipper - Evolve Wingull / Routes 103, 104, 105, 106, 107, 108, 109, 110, 115, 118, 119, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, and 134, Dewford Town, Ever Grande City, Lilycove City, Mossdeep City, Pacifidlog Town, Slateport City

Ralts - Ruby, Sapphire, or Emerald; Route 102 / XD; ONBS

Kirlia - Evolve Ralts

Gardevoir - Evolve Kirlia

Surskit - Ruby or Sapphire; Routes 102, 111, 114, 117, and 120 / XD; Oasis Poke Spot

Masquerain - Evolve Surskit

Shroomish - Ruby, Sapphire, or Emerald; Petalburg Woods / XD; Cipher Lab

Breloom - Evolve Shroomish

Slakoth - Ruby, Sapphire, or Emerald; Petalburg Woods

Vigoroth - Evolve Slakoth

Slaking - Evolve Vigoroth

Nincada - Ruby, Sapphire, or Emerald; Route 116

Ninjask - Evolve Nincada

Shedinja - Evolve Nincada

Whismur - Ruby, Sapphire, or Emerald; Route 116, Rusturf Tunnel, Victory Road (Also availabe in Desert Underpass in Emerald)

Loudred - Evolve Whismur / Ruby, Sapphire, or Emerald; Victory Road (Also available in Desert Underpass in Emerald)

Exploud - Evolve Loudred

Makuhita - Ruby, Sapphire, or Emerald; Granite Cave, Victory Road (Also available via in-game trade in Rustboro City in Ruby or Sapphire) / Colosseum; Phenac City / XD; ONBS

Hariyama - Evolve Makuhita / Ruby, Sapphire or Emerald; Victory Road

Azurill - Breed Marill or Azumarill

Nosepass - Ruby, Sapphire, or Emerald; Rock Smash in Granite Cave / XD; Pyrite Colosseum, Realgam Colosseum, Poke Spots

Skitty - Breed Delcatty / Ruby, Sapphire, or Emerald; Route 116 (Also available via in-game tradein Fortree City in Ruby or Sapphire)

Delcatty - Evolve Skitty / XD; Cipher Lab

Sableye - Sapphire or Emerald; Granite Cave, Cave of Origin, Sky Pillar, Victory Road / XD; Citadark Isle

Mawile - Ruby or Emerald; Victory Road (Also available in Granite Cave, Cave of Origin, Sky Pillar in Ruby) / XD; ONBS

Aron - Ruby, Sapphire, or Emerald; Granite Cave, Victory Road / XD; Cave Poke Spot

Lairon - Evolve Aron / Ruby, Sapphire, or Emerald; Victory Road

Aggron - Evolve Lairon

Meditite - Ruby or Sapphire - Mt. Pyre, Victory Road / Colosseum; Pyrite Cave / XD; In-game trade in Pyrite Town

Medicham - Evolve Meditite / Ruby or Sapphire - Victory Road

Electrike - Breed Manectric / Ruby, Sapphire, or Emerald; Route 110, Route 118

Manectric - Evolve Electrike / Ruby, Sapphire, or Emerald; Route 118 / XD; Citadark Isle

Plusle - Ruby, Sapphire, or Emerald; Route 110 (Also available via in-game trade in Fortree City in Emerald) / Colosseum; Pyrite Town

Minun - Ruby, Sapphire, or Emerald; Route 110

Volbeat - Ruby, Sapphire, or Emerald; Route 117

Illumise - Ruby, Sapphire, or Emerald; Route 117

Roselia - Ruby or Sapphire; Route 117 / XD; Phenac City

Gulpin - Ruby, Sapphire, or Emerald; Route 110 / XD; Cipher Lab

Swalot - Evolve Gulpin

Carvanha - Ruby, Sapphire, or Emerald; Route 118, Route 119 / XD; Cipher Lab

Sharpedo - Evolve Carvanha / Ruby, Sapphire, or Emerald; Routes 103, 118, 122, 124, 125, 126, 127, 129, 130, 131, 132, 133, and 134, Mossdeep City, Pacifidlog Town

Wailmer - Ruby, Sapphire, or Emerald; Routes 103, 105, 106, 107, 108, 109, 110, 115, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, Dewford Town, Ever Grande City, Lilycove City, Mossdeep City, Pacifidlog Town, Seafloor Cavern, Shoal Cave, Slateport City

Wailord - Evolve Wailmer / Ruby, Sapphire, or Emerald; Route 129

Numel - Ruby, Sapphire, or Emerald; Route 112, Fiery Path, Jagged Pass / XD; Cipher Lab

Camerupt - Evolve Numel

Torkoal - Ruby, Sapphire, or Emerald; Fiery Path (Also available in Magma Hideout in Emerald)

Spoink - Ruby, Sapphire, or Emerald; Jagged Pass

Grumpig - Evolve Spoink

Spinda - Ruby, Sapphire, or Emerald; Route 113

Trapinch - Breed Vibrava or Flygon / Ruby, Sapphire, or Emerald; Route 111 (Also availabe in Mirage Tower in Emerald) / XD; Rock Poke Spot

Vibrava - Evolve Trapinch / Colosseum; Shadow Pokemon Lab

Flygon - Evolve Vibrava

Cacnea - Ruby, Sapphire, or Emerald; Route 111

Cacturne - Evolve Cacnea

Swablu - Breed Altaria / Ruby, Sapphire, or Emerald; Route 114, Route 115 / Colosseum; Pyrite Cave

Altaria - Evolve Swablu / Ruby, Sapphire, or Emerald; Sky Pillar / XD; Citadark Isle

Zangoose - Ruby; Route 114 / XD; Cipher Key Lair

Seviper - Sapphire or Emerald; Route 114

Lunatone - Sapphire; Meteor Falls / XD; Phenac Stadium

Solrock - Ruby or Emerald; Meteor Falls / XD; Citadark Isle

Barboach - Ruby, Sapphire, or Emerald; Route 111, Route 114, Route 120, Meteor Falls, Victory Road

Whiscash - Evolve Barboach / Ruby, Sapphire, or Emerald; Meteor Falls, Victory Road

Corphish - Ruby, Sapphire, or Emerald; Route 102, Route 117, Petalburg City

Crawdaunt - Evolve Corphish

Baltoy - Ruby, Sapphirem or Emerald; Route 111 / XD; Cipher Lab

Claydol - Evolve Baltoy / Ruby, Sapphire, or Emerald; Sky Pillar

Lileep - Ruby, Sapphire, or Emerald; Revive Root Fossil from Route 111 in Rustboro City

Cradily - Evolve Lileep

Anorith - Ruby, Sapphire, or Emerald; Revive Claw Fossil from Route 111 in Rustboro City

Armaldo - Evolve Anorith

Feebas - Ruby, Sapphire, and Emerald; Six random tiles of water on Route 119 will allow you to encounter Feebas if you fish on them.

Milotic - Evolve Feebas

Castform - Ruby, Sapphire, or Emerald; Weather Institute

Kecleon - Ruby, Sapphire, or Emerald; Routes 118, 119, 120, 121, and 123

Shuppet - Ruby, Sapphire, or Emerald; Mt. Pyre (Also available in Route 121, Route 123 in Sapphire or Emerald)

Banette - Evolve Shuppet / Sapphire or Emerald; Sky Pillar / XD: Citadark Isle

Duskull - Ruby, Sapphire, or Emerald; Mt. Pyre (Also available in Route 121, Route 123 in Ruby) / XD; ONBS

Dusclops - Evolve Duskull / Ruby; Sky Pillar

Tropius - Ruby, Sapphire, or Emerald; Route 119 / Colosseum; Realgam Tower

Chimecho - Ruby, Sapphire, or Emerald; Top of Mt. Pyre

Absol - Ruby, Sapphire, or Emerald; Route 120 / Colosseum; Realgam Tower

Wynaut - Breed Wobbuffet / Ruby, Sapphire, or Emerald; Hatch egg from Lavaridge Town, Mirage Island

Snorunt - Ruby, Sapphire, or Emerald; Shoal Cave (low tide) / XD; Phenac City

Glalie - Evolve Snorunt

Spheal - Ruby, Sapphire, or Emerald; Shoal Cave / XD; Cipher Lab

Sealeo - Evolve Spheal

Walrein - Evolve Sealeo

Clamperl - Ruby, Sapphire, or Emerald; Underwater

Huntail - Evolve Clamperl

Gorebyss - Evolve Clamperl

Relicanth - Ruby, Sapphire, or Emerald; Underwater

Luvdisc - Ruby, Sapphire, or Emerald; Route 128, Ever Grande City

Bagon - Breed Salamence / Ruby, Sapphire, or Emerald; Meteor Falls

Shelgon - Evolve Bagon

Salamence - Evolve Shelgon / XD; Citadark Isle

Beldum - Breed Metagross / Ruby, Sapphire, or Emerald; Steven's House in Mossdeep City

Metang - Evolve Beldum

Metagross - Evolve Metang / Colosseum; Realgam Tower

Regirock - Ruby, Sapphire, or Emerald; Desert Ruins

Regice - Ruby, Sapphire, or Emerald; Island Cave

Registeel - Ruby, Sapphire, or Emerald; Ancient Tomb

Latias - Sapphire or Emerald; Roaming

Latios - Ruby or Emerald; Roaming

Kyogre - Sapphire; Cave of Origin / Emerald; Marine Cave

Groudon - Ruby; Cave of Origin / Emerald; Terra Cave

Rayquaza - Ruby, Sapphire, or Emerald; Sky Pillar

Jirachi - Can only be acquired through the Pokemon Colosseum Bonus Disc (US) or Pokemon Channel (EU).

Deoxys - Impossible to obtain, unless you attended an AuroraTicket distribution event.

Now that you know all of your possible options for obtaining each Pokemon, let's run through which options are the easiest, quickest, and most cost-efficient. As mentioned at the top of this post, there are some games that are required no matter what. These games are Pokemon Leaf Green, Pokemon XD; Gale of Darkness, and Pokemon Colosseum. In addition to these three games, you will also need two of Pokemon Ruby, Pokemon Sapphire, or Pokemon Emerald. I chose Ruby and Sapphire, because I already owned those two games, but any two of those three will work.

Problem Pokemon:

There are so Pokemon that are difficult to obtain, and will alter decision making when it comes to which games to play, what order to play them in, etc. These Pokemon are...

Ho-Oh
Huntail / Gorebyss
Kabuto / Omanyte
Anorith / Lileep
Bulbasaur / Charmander / Squirtle
Treecko / Torchic / Mudkip
Jirachi
Mew
Celebi
Deoxys

I included Ho-Oh on this list just because he is by far the most annoying Pokemon to obtain. There is only one way to obtain him, and it's pretty absurd. First you need to complete Pokemon Colosseum. Then you need to purfiy ever shadow Pokemon in the game. That alone should take a very long time, but we haven't even gotten to the most tedious part yet. After purifying every shadow Pokemon, you need to defeat ONE HUNDRED trainers IN A ROW in Mt. Battle. Yikes.

The bottom four Pokemon on the list are pretty much unobtainable. American players can get Jirachi if they have the Pokemon Colosseum Bonus Disc (which can be purchased online for around $40 to $50 if you really want Jirachi that bad) and European players can get Jirachi from Pokemon Channel. Japanese players can get Celebi from the Pokemon Colosseum Bonus Disc. Mew and Deoxys are completely unobtainable unless players attended events years ago.

The other Pokemon on the list are problem Pokemon because while they can all be obtained, only one Pokemon per line can be obtained organically on each save file. Only one starter Pokemon can be chosen in each game, you can only choose one of the two fossils, and you can only choose one of the DeepSeaTooth or DeepSeaScale. In order to avoid these problems, you will need to reset some of your games, or go out and buy additional copies (which seems like a waste of money to me).

So, without further ado, here is the method that I recommend, as I have found it to be the easiest, quickest, and most cost-efficient.

Step 1: Play through one of the Hoenn games (either Ruby or Sapphire) and catch everything you can. Evolve everything and fill up the Pokedex as much as possible. This will be the game that you complete the Pokedex on. For any Pokemon that evolve through trading, trade them to another game and then back. When you finish this step, your Pokedex should be at 183.

Step 2: Start up your second Hoenn game (either Emerald, or whichever of Ruby and Sapphire you didn't use in Step 1). Choose a starter other than the one you chose in Step 1, trade it to the game from Step 1, then reset your game. Pick the third starter, and play through until the end. Catch all of the version exclusives not available in the game from Step 1, pick the other fossil, and choose whichever Clamperl evolutionary item you didn't choose in the game from Step 1. If your second game is Emerald, do not worry about the Johto Pokemon in the Safari Zone. You will need to catch Pokemon from their evolutionary line later on anyway, so catching them now would be a waste of time. Trade everything over to the game from Step 1, and evolve it all. Your Pokedex should now be at 200 if your second game is Ruby or Sapphire, and 199 if you second game is Emerald.

Step 3: Start up Pokemon Leaf Green. Catch everything and send it over to the game from Step 1. The only Johto Pokemon from the post-game (Sevii Islands) that you need to catch is Unown. Everything else can be acquired through Colosseum or XD. Then reset your Leaf Green save file, pick a different starter than the one you chose the first time, and send it to the game from Step 1. Restart your Leaf Green save file again, and pick the third starter. When you get to Mt. Moon, choose the other fossil. Play through until you get to Cinnabar Island, where you can revive the fossil, and then send the starter and fossil Pokemon over to the game from Step 1. Evolve everything on the game from Step 1.

Step 4: Start playing Pokemon XD: Gale of Darkness. Catch all of the shadow Pokemon, including Lugia. Purify the ones you need, and tranfer them over to the game from Step 1. Do any necessary breeding or evolving.

Step 5: Start playing Pokemon Closseum. Catch all of the shadow Pokemon and purify them all. Then start your Mt. Battle challenge. Once completed, transfer all necessary Pokemon over to the game from Step 1, and do any breeding or evolving that you need to do. After this, your Pokedex should be at 382, with the 4 missing Pokemon being Mew, Celebi, Jirachi, and Deoxys.

Step 6 (optional): Transfer Jirachi onto your game from the Pokemon Colosseum Bonus Disc if you have the disc or feel like spending money to get one additional Pokemon.

And that's it! You've completed the Pokedex (well, except for some of the mythical Pokemon). If anyone actually does this, please share down below, I'd love to see your Pokedex and hear about your experience. If you have any questions, please feel free to ask! Thank you for reading, and good luck!

I would like to add an addendum to this. As you can make it a heck of a lot easier on yourself if you're both willing to spend the money, and or hack a Wii. Also making Celebi 100% legitimate to capture in American games.

Celebi
Requirements:

1 Japanese Ruby/Sapphire Cartridge.
2. 2 GBA Systems
3. Japanese Gamecube or hacked Wii with Nintendon't
4. Japanese Colloseeum Bonus Disc.
5. GBA to Gamecube Adapter.

Step 1:
Connect GBA to either the Japanese gamecube with a 100% Japanese coliseum save file. Make sure a Japanese version of Ruby or Sapphire is inserted. Or connect to a old modded Wii with gamecube ports with save .raw file containing Japanese save file.

Step 2:
Boot the bonus disc on the GameCube or Wii with Nintendon't

Step 3: Follow the regular instructions on how to obtain one, but make sure the Coliseum save has one empty party slot, as it first gives the celebi to the Coliseum save before the Gen 3 save.

Step 4: Receive the Celibi to your Gen 3 game. (Should have obtained the Pokedex and have an empty party slot)

Step 5: Connect your two GBA's with a link cable. One containing a English cart, one containing the Japan cart with Celebi. Trade Pokémon normally done with any game of that gen, a misconception that most have is that you can't cross trade between regions, but you can quite easily.

Step 6: Enjoy Celebi on your english cart!


Deoxys

Requirements:
1. 2 GBA systems.
2. GBA Link Cable
3. FireRed/LeafGreen cartridge.
4. EZFlash Omega or Everdrive GBA X5

A distribution rom of the Aurora Ticket can be found online, loading it in a GBA flashcart, you can receive it only on a copy of FireRed or LeafGreen cart due to it not being the one compatible with Emerald. After receiving it, you can catch Deoxys and trade it to your game of choice. Can't provide it here as it is a copyrighted rom, but good old Google could get it for ya.

Pokemon BOX

Pokemon BOX is a GameCube game that was the predecessor to Pokemon Bank, saving it to the gamecube memory card rather than the cloud. Making transferring boxes upon boxes of Pokemon much easier and completely bypassing the what I call "Great Magikarp Migration".  Bad news is that it's like $100-200, so either deal with the "Great Magikarp Migration" or DO WHAT YOU WANT CAUSE I PIRATE IS FREE with Nintendon't.

On top of the possible ways to get Celebi and Deoxys that Boured discussed, I'd also to add that it is technically possible to get the four mythical Pokemon by using a very elaborate glitch in Pokemon Emerald that revolves around the Pomeg Berry. I didn't mention this in my original post, because I'm not sure if it's considered a legitimate method or not, but it doesn't require anything other than a Game Boy Advance and a copy of Pokemon Emerald to do it. It is a very complex and unstable glitch though, so be prepared for it to potentially screw up your save file, and/or not work.

I don't quite understand the glitch myself, but if you search for things like "Pomeg Berry Glitch" on YouTube you can find a bunch of videos on it. I'd like one, but there isn't one specific video that really covers the glitch in its entirety.