Sometimes Mega Man 4 can be a hard game, one reason is because of the bosses and their ridiculous amount of health or  their strong attacks. This is a guide to help you know their weaknesses and attacks to defeat them easily.

The first boss you should take down is toad man. Normally he is weak to Drill cannon, but the mega buster works fine. Toad man jumps around the room and if you take too long to hit him he will use Rain Flush and deal 5 pixels of damage to you. Defeating him gives you the Rain Flush which if shot will cause it to make it rain and kill everything on screen.

Bright Man is the boss you would want to defeat next since he is weak to Rain Flush. Bright man is extremely fast and will jump around the room which makes him hard to hit. Occasionally he will freeze time to jump and shoot at you which deals about 2 pixels of damage. Defeating him gives you the Flash stopper and unlike in Mega Man 2, this time you can freeze time and shoot things.

Pharaoh Man is the next boss you want to take on, but their is a secret weapon in his stage that is really helpful. If you manage t jump the gap leading to the underground section and move all the way to the right you will find another section containing the Balloon which you can use in tight situations in Vertical sections. Pharaoh Man himself is not really weak to the Flash stopper which he isn't weak against, but he'll just be frozen in time until it ends. His attacks are to jump around and use the Charged Pharaoh Shot. Defeating him also gives you the Pharaoh shot which is a normal shot at first, but if charged (Hold B) it will float over your head and turn into a huge Pharaoh Shot.

Ring Man is the one you want to take on next is Ring man since he is weak to Pharaoh Shot. Ring Man is another extremely fast boss and will jump around even diagonally and use Ring Boomerang. Defeating him gives you the ring boomerang which is just a boomerang.

Dust Man is best to take on next since he is weak to Ring Boomerang. Dust man can use a built-in vacuum to pull you towards him to damage you. He also uses his dust crash which will be shot then explode into 4 pieces if it hits a wall. Defeating him gives you the dust crash which i just explained.

Skull Man is who you want to take down next since he is weak to Dust Crash. Skull Man Runs around the room while shooting you and using his skull barrier so you can't hit him. Defeating him gives you the Skull Barrier which is a simple shield Weapon.

Dive man is who you want to take on next, but first there is a secret item in his stage. If you fall down the pit after the second whale mini-boss then there will be a series of spikes and if you manage to make it to the bottom you get the wire which can shoot up and be used as a grappling hook. Dive Man himself is weak to Skull Barrier and will dive around the room and shoot missiles. Defeating him gives you the Dive Missile which is a honing Missile.

Drill Man is the last of the robot masters you want to to take on and is weak to dive missile. He dives into the ground and if you are in the same spot as him he'll drill up and deal about 2 pixels of damage. Defeating him gives you Drill Cannon which can be shot and if the fire button is pressed again, it can explode.

Dr. Cossack Stage 1's boss, Mothraya, is weak to Ring Boomerang, but can only be hit on a glowing orb on its body. Mothraya uses the spike it has to break the floor and maybe damage Mega Man too.

Dr. Cossack Stage 2's Boss, Square Machine, is weak to Dust Crash, but like Mothraya it can only be hit on the glowing orb in the center. Square Machine splits into 3 parts and dashes across the room and might crush you without perfect timing. When the Machine slows down, jump into one of the parts and you'll be in the machine and can finally hit it only the platforms it gives you, but it will shoot at you to try and knock you off.

Dr. Cossack Stage 3's boss, the Cockroach twins, are weak to Pharaoh Shot and will just move around the walls and shoot.

Dr. Cossack Stage 4's boss, The Cossack Catcher, Is weak to Dust Crash and will grab you with a claw to hurt you.

Dr. Wily Stage 1's boss the Metall Daddy is weak to Pharaoh Shot and will jump to crush you which can hurt Mega Man quite a bit. He will also produce more Metalls which is annoying.

Dr. Wily Stage 2's boss, Tako Trash, is weak to Ring Boomerang, but of course only on the glowing orb on its body. It will shoot at you as you try to use the platforms to hit him.

Wily Stage 3 has a Boss Rush and Wily Machine 4. Wily Machine 4 Form 1 is weak to Ring Boomerang and Form 2 is weak to Drill Cannon and must explode to hit the machine properly. 

The Final Wily Stage's boss, Wily Capsule, is weak to Pharaoh Shot and will summon 4 energy balls to hit you and teleport around the room randomly.

Hope this guide helped you with the bosses and that they will be no trouble for future playthroughs of Mega Man 4.

Wow this is a good guide. Though I have not played megaman before sadly. I can see this helping those who would be stuck on these bosses. Good job. ^-^