In Rise of the Teenage Mutant Ninja Turtles, Hypno-Potamus is a stage magician who was mutated into a hippopotamus. He is an opponent of the Turtles, and the roommate and love interest to fellow antagonist Warren Stone.
As a human
Mezmer-Ron is a short plump human with caramel skin, light brown eyes, black hair, eyebrows and goatee. He wears a pink turban with a red-rimmed black stone, a purple dress coat, white shirt with a red bow tie and sash, white gloves, dark blue pants and black dress shoes. He also has a gold hoop earring on his left ear.
As a mutant
Hypno-Potamus is a large mutant hippo with dark grey skin and yellow eyes with red pupils. He retains his black hair and goatee, and wears the same outfit he wore prior to his mutation.
Hypno-Potamus was previously a successful stage magician and hypnotist by the name of Mezmer-Ron, who performed magic tricks with a hippopotamus named Doug. During a performance he was mutated after being stung and injected with ooze by one of Baron Draxum's Oozesquitoes, which the Turtles and April O'Neil had accidentally released into the city. Because of the presence of his animal partner Mezmer-Ron transformed into a humanoid hippopotamus and began stealing the signature animals of other stage magicians.
The Turtles attempted to capture him using a hippo costume and the scent of a female hippo. Hypno-Potamus found them just as Warren Stone was trying to entrap and kill them, and attempted to romance a hippo-suited Michelangelo. When the ruse was revealed, he began battling the Turtles, and eventually used his hypnotic powers to mesmerize them. He tried to kill Michelangelo first, but was thwarted by Warren, who used his blue jewel to reflect the hypnotic power back at Hypno-Potamus. This put Hypno-Potamus in a trance, allowing the Turtles to capture him.
Since then, Hypno-Potamus has been pursuing every successful illusionist out of pure envy, or trying to trump his competition (often with very definitive methods). He is also looking for a way to somehow bring Doug back to life, who has disappeared since his mutation.
Hypno-Potamus has the ability to put his enemies in a trance with hypnotic powers, which he unleashes by shouting "Mezmer-rooooo!". He levitates and manipulates objects like several metal hoops, which are often used in magic tricks.
- Baron Draxum: Hypno was one of Draxum's recruits for the Evil League of Mutants, and they were briefly allies. But they have become enemies as of Warren & Hypno, Sitting in a Tree, since Draxum attacked the apartment he shares with Warren Stone to seize Warren's gauntlet Charlotte, then later walked back an agreement with Hypno to spare Warren's life in exchange for the Turtles and the gauntlet, and then tried to execute Warren in front of Hypno. After this, Hypno furiously fought Draxum in defense of Warren's life.
- Warren Stone: They were both fellow members of the Evil League of Mutants led by Baron Draxum. By the episode "Warren and Hypno, Sitting in a Tree", they are revealed to have become friends, moved in together and fallen in love. They characterize their relationship as "friends/roomies/magical assistants," but are extremely tactile and affectionate with each other, very visibly treating each other like boyfriends.
- The Turtles and April O'Neil: Hypno-Potamus was originally an enemy of the Turtles, but after Baron Draxum attacked him and Warren Stone in Warren & Hypno, Sitting in a Tree, Hypno initially agreed with Draxum to let Hypno and Warren go free if they helped capture the Turtles and hand over Warren's gauntlet. But Draxum went back on his word and seized everyone. When it was clear Draxum would kill Warren, Hypno struck up a temporary alliance with the Turtles to save Warren's life. Once Warren was safe, Hypno parted with the Turtles in peace and took Warren home. With the upset of alliances and enmities, it is no longer clear what relationship Hypno has with the Turtles.
- His human stage name, "Mezmer-Ron," is a play-on the word "mesmerize", which is also a synonym of the word "hypnotize".
- He is an experienced juggler.
- Hypno-Potamus has a running gag of recalling several landmarks and cultural references to New Zealand, the home country for his voice actor, Rhys Darby.
- Hypno-Potamus has shown a romantic interest in both men and women (meaning he's bisexual).