When people think of powerful gym leaders in Pokemon, many will think of the ones you encounter later in the game. It makes sense, they are the highest leveled after all. But I'd argue some of the tougher gym leaders in the franchise actually come from the other side of the equation. An earlier gym leader might be lower leveled, but you won't have access to many evolutions, moves, etc. yet to help you in your battle. I'm thinking of gym leaders like Whitney from Johto, or Flannery from Hoenn. And in the city of Eterna in the Sinnoh region, I think another gym leader can fit this description.

Pokemon Diamond, Pearl, Platinum, Brilliant Diamond, Shining Pearl

Gardenia is a Grass type expert and the leader of the Eterna City Gym. A grass type leader sounds pretty simple. The type is weak to so much, and a lot of the grass Pokemon just aren't as strong as the others, at least offensively. Gardenia isn't just an easy opponent, however.

Gardenia is one of the gym leaders who received a gym redesign in the jump from Diamond and Pearl to Platinum. In the originals, her gym was like a hedge maze. You had to find all her trainers before she would let you battle her. In Platinum, there is a big flower in the center of the gym. The petals of this flower act like clock hands, and you have to rotate around the flower until you make your way past her trainers and to Gardenia. Pretty fun gym designs!

Once you finally get to her, she will accept your challenge. Gardenia uses three Pokemon. In Diamond, Pearl, Brilliant Diamond, and Shining Pearl, she starts the battle with a Cherubi. This is a Grass type native to Sinnoh that can be found by using Honey on yellow Honey trees. It takes a while to obtain one so many players will see it here for the first time. Her next Pokemon is a Turtwig, the Grass type starter of the region! I believe this is the only time a gym leader uses one of the region's starter Pokemon, so pretty neat! They aren't very strong though, so you won't struggle. Turtwig can set up a Reflect to lower your damage, so special attacks are better.

In Platinum she changes the order a bit. She leads with Turtwig this time. It's not a big threat, but it does use a weird move: Sunny Day. Setting up the Sunlight sounds like it's bad for a Grass leader, as Fire will deal even more damage. It makes more sense when you get to her second Pokemon. Instead of the weak Cherubi, Gardenia sends out its evolved for Cherrim! Cherrim has a unique ability that changes its form in the Sunlight. It gains a Special Defense boost as well, on top of a.... attack buff? But it's a Special Attacker... It's still neat to see her show off Cherrim's unique quirk.

In all games, her final Pokemon will be Roserade. Roserade is the brand new Sinnoh evolution for Roselia, a Hoenn Pokemon. Sinnoh is kind of famous for adding a bunch of evolutions to older Pokemon, this being one of them. Roserade is insanely strong for this point in the game, with massive stats and strong moves in Grass Knot and Magical Leaf. Even Pokemon that resist Grass end up taking a lot of damage. It can also spread Paralysis or Poison on top of that.

Defeating Gardenia gets you the Forest Badge. Gardenia is not seen again after this in the main story. She can, however, be found in the Eterna Forest after defeating her. She will stand in front of some Cut trees, warning the player of the Haunted Mansion that lies beyond them. Gardenia is absolutely terrified of Ghost type Pokemon, and will do anything to get away from them. I'm almost convinced she put those Cut trees there to keep them away.

In Pokemon Platinum, she can be rematched in the Post-game in the Survival zone on an island separate from the Sinnoh mainland. She keeps her now fully evolved Gym Team, while also adding a Jumpluff and a Bellossom. She heavily focuses on setting up the Sun and using Pokemon with Chlorophyll as their ability to deal big damage.

In Brilliant Diamond and Shining Pearl, Gardenia can be rebattled in her gym instead. She ditches Bellossom here in favor of a Sunflora and a Breloom. It's a bit of a shame that she doesn't use any other new Sinnoh grass types in either rematch. She can also be battled in the Battle Tower, teaming up with Ghost gym leader Fantina in the Double Battle mode, or being fought solo in the Single Battle mode.

Pokemon Black 2, White 2

Gardenia returns alongside her fellow Sinnoh Gym Leaders for the Pokemon World Tournament. She can be fought in the Sinnoh Leaders and Type Experts challenges. She finally uses some Sinnoh originals in these battles! Leafeon, the Grass type evolution of the popular Eevee, makes an appearance. Also on her team are the new Carnivine and Tangrowth, the evolution of the classic Tangela.

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Gardenia is a more quiet character compared to some of Sinnoh's other gym leaders. Still, I love her design (her outfit is one of my all time favorites), and I like her gym designs a lot as well.

I wish she was given more story content, but at least the running gag with her being scared of Ghost types is kind of funny. She even mentions at some point that she'd have no idea what to do if a Grass/Ghost type Pokemon got discovered. I hope she has an answer to that, because there are several now.