The Humilau Gym made its anime appearance in The Road to Humilau!. It is a seaside Gym with a rectangular battling field having two raised platforms on the opposite ends. A Trainer named Cameron challenged Marlon for a Gym battle and won, earning himself the Wave Badge, and completed all the eight Badges required to participate in the Unova League.
Jellicent was the first Pokémon Marlon used against Cameron in their Gym battle. He battled Cameron's Ferrothorn, and after being defeated by Ferrothorn's Thunderbolt, his Ability activated, disabling the move.
Mantine is Marlon's ace Pokémon. It was the second Pokémon Marlon used against Cameron in their Gym battle. It quickly knocked out Ferrothorn with a combination of Wing Attack, Bullet Seed, and Psybeam. Afterwards, Mantine faced Cameron's Samurott and was knocked out without landing a single attack on her.