Marlon appears in Pokémon Black 2 and White 2 as the eighth and last Gym Leader that the player challenges. He is a big-hearted Pokémon Trainer who gives passionate advice. Marlon also seems to be a very relaxed and carefree man, as shown by his obliviousness as to who Team Plasma are and what they do. He asks the player if Team Plasma are bad people.
Marlon specializes in Water-type Pokémon. Upon defeating him, he will reward the player with a Wave Badge and TM55 (Scald). Outside of battle, Marlon is a fisherman who catches Water-type Pokémon which he would later use in future Gym battles.
Upon arriving in Humilau City, Marlon is absent from the Gym, and the player is sent to find him. The player meets Marlon just as they head north of the Gym, in which he returns to it and awaits a Gym battle. After the Gym battle, Marlon jumps into the ocean and swims away. Upon exiting the Gym, Hugh walks up and congratulates the player on gaining all eight of Unova's Gym Badges, and then their attention turns to Team Plasma, during which Marlon walks up and asks about them.
He heads off to the Seaside Cave to find the Plasma Frigate. Later on on Route 21, he is seen jumping off the Plasma Frigate after lowering the boarding plank, and then heads back to the Gym, leaving the player and Hugh to deal with Team Plasma.
"Sup, you must be here to challenge the Pokémon Gym! I'm the Gym Leader, Marlon. Sorry to make you look for me, yo. I was swimmin' with the Pokémon, and it felt real good, so I kept goin' and goin'. I'll be waitin' in the Gym, 'K?"
"Hey, friends! Team Plasma's not botherin' me. They could be up to no good for reals, and... It's not my style to go around decidin' Team Plasma's bad without thinkin' 'bout it just 'cause everyone says so! But, eh, you're havin' trouble, so I've got to help out! That's what I want to do!"
"Listen, 'K. Believe in somethin'! Searchin' for stolen Pokémon is fine! Keepin' Unova from bein' iced over's fine too! It's all good. But think 'bout why you're doin' that. The strength of your beliefs is what gives you and your Pokémon power! I made some noise, so some people came out! Hey, be careful, 'K!"
If talked to
If talked to (post-game)
"Waves can be rough of calm, but it's still the same sea! Eh, there're lots of ways to look at the same thing!"
"I'm strong like the ocean's wide. You're gonna get swept away, fo' sho'. Eh, that's enough talk! I'll prove it! Let's get started, 'K?"
Before battle (final round)
"Oh ho, so I'm facing you! That's off the wall. How 'bout you and I make some waves and sweep the audience away? Let's leave 'em with even bigger smiles!"
"You're strong as a gnarly wave and as nice as a glassy sea."
If the player is defeated
"You're tough, but it's not enough to sway the sea, 'K!"
After being defeated
"You don't just look strong--you're strong fo' reals! Eh, I was swept away, too!"
"The tide comes in an' out, and in life you win and lose! What's important is that it keeps goin'."
In the lobby, after the tournament
"Eh, right now, you're like a ragin' sea that washes everythin' away! Uihaa! What a great battle, yo!"
It's cliché to compare life to a rough sea, but don't be swept away!
Jingle: "Woo hoo! All right! It's 'The National Gymquirer'!"
Page: "That's right! We collect the hottest gossip about Gym Leaders seen around town! Here is today's letter. From someone going by the name MisterFisher! Thank yooou! 'Marlon was swimming the other day, and he just kept going faster until he shot out of the water and into the sky! That swimming style could completely dominate the world of swimming.' Hm... That is amazing, but nobody else can do that. Actually, can you even call jumping into the sky swimming? 'The National Gymquirer'! We eagerly await your letters!"
Marlon appeared in The Road to Humilau!, where Cameron aimed to challenge his Gym for his final Badge. After Cameron and Ash lost their way to Humilau City, Marlon found the two Trainers and took them to his Gym. There, Marlon faced Cameron in a Gymbattle. Although Marlon had a powerful team, he was defeated by Cameron's Samurott, giving Cameron his last Gym Badge.
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.
Marlon makes his first appearance as a competitor in the Unova Pokémon League. There, he makes it to the top 8 and is set up against Hood Man as his opponent. In the battle, Marlon proves to be a powerful opponent, but is ultimately defeated and eliminated from the tournament. Afterward, Marlon decides to leave, only to be approached by White. When White asks him for information about the mysterious Hood Man, Marlon reveals that the Trainer made it to the League without even collecting any Badges. Despite this, Marlon tells White that she should focus her investigations on Cheren because he seems even more suspicious than Hood Man.
It is revealed Marlon was made the Gym Leader of Humilau City. In PS541, Marlon and Benga rescue Benga's classmates at the Aspertia CityTrainers' School from Castelia City, which had been frozen by the Plasma Frigate. After taking everyone to the Marine Tube, Benga assists everyone recuperate from the cold. Once everyone had woken up, Marlon and Benga explain the situation and reveal that they are gathering forces to help launch a counterattack against Team Plasma, who have been freezing other cities across Unova.
Frillish → Jellicent ♂
Jellicent is Marlon's only known Pokémon. He has been with Marlon ever since he was a Frillish. Marlon used him to battle Hood Man's Beheeyem at the Unova Pokémon League. Although he put up a good fight, Beheeyem defeated him with Shadow Ball, making Hood Man the winner. Later, he was healed by White's Nancy in an attempt to get Marlon's trust.