Maylene is the third Gym Leader encountered in Diamond and Pearl and the fourth in Platinum. In Diamond and Pearl, to get to Maylene, the player must not only beat her trainers, they have to move sliding walls. In Platinum the player must beat trainers and push punching bags to knock over weights.
Maylene can also be challenged to a battle in the Survival zone on most days in the Platinum version.
In the anime
Maylene made her debut in Lost Leader Strategy! where she decided to quit the Gym after she lost her Gym Battle with Paul and her confidence. She ran away from her duties. Dawn felt the same way she did and inspired her not to give up. She then requested that she have a Gym Battle with her.
In Crossing the Battle Line! Maylene had her battle with Dawn. The plan for Dawn was to lose yet give it her all to get Maylene's confidence back. When the first battle began Maylene copied the moves her Pokémon used as she was giving the orders to do so (She said and did a Drain Punch attack just as her Meditite did). She knocked out her Buneary but lost to her Piplup. Maylene then pointed out that Dawn treated the battle like she did a contest. During the battle between Piplup and Lucario, Maylene was starting to get back in synch with her Pokémon. She beat Dawn and got her confidence back.
In A Triple Fighting Chance! She had her Gym Battle with Ash. However, this battle ended in a draw, but Maylene felt so good that she thought Ash deserved Cobble Badge.
"Hello. I'm pleased to meet you. I'm Maylene, and I'm the Gym Leader. I don't really know what it means to be strong, or how I got to be the Gym Leader. But I will do the best I can as the Gym Leader. I take battling very seriously. Whenever you're ready!"
After sending out last Pokémon
"Oh! But this isn't the end, my friend!"
"I'm in a bit of a bind, aren't I?"
"I shall admit defeat... You are much too strong."
After being defeated
"...OK. You win. That was a tough loss. I learned a lot from it. Please, accept this Gym Badge."
"Gee, I'm hungry... Oh, excuse me. I'm too busy to help you now. Gotta go have a lunch break. <Player>, I can't explain what it means to be strong. I don't know how much effort goes into being strong... But being with Pokémon lets us keep making the effort, doesn't it?"
"Oh, <player>! Um, are you maybe on your way to Snowpoint City? That's where I'm going, too. If I use Fly, I can get there instantly, but I'm walking for my training. I have no problem with this. I'm used to the cold because I go barefoot and lightly dressed because I think it's healthier to do that. But I should use snowgear, too. I'll be going now. Please take care!"
Snowpoint City Pokémon Center
"Brrr... Good thing I brought snowboots...Oh, hi, <player>! Are you taking the Gym challenge now? I'm hoping to see Candice soon, but I'm staying put until I warm up again first. Oh, you should know that Candice is a user of Ice-type Pokémon. I really admire Candice. She's so studious. She wanted to practice against me to learn about the Fighting type. It's because the Ice type matches up badly against the Fighting type."
"...Um, your Villa... Would it be OK if I took a look around?"
"<Player>, please hear how my training is going. Thanks to my training, I'm beginning to understand the feelings of Pokémon. It lets me choose moves with much more confidence!"
"<Player>, please hear how my training is going. Thanks to my training, my handwriting has improved tenfold! ...Yes. It has absolutely nothing to do with how strong I am as a Gym Leader."
"...You know those Accessories for Pokémon? Would it be funny if someone were to wear those?" (to Candice)
"...! You-you mean it? Th-thank you so much!" (to Candice)
"What makes a Gym Leader a good one?" (to Candice)
HeartGold and SoulSilver
"Munch munch munch... The eatathon contest! I never dreamed of such a wonderful thing. After a strict diet of training, I can eat like a Hippowdon. The winner eats for free, too. That's just a dream come true!"