Mayhem, also known as Agent 64, is a character appearing in the first season of Rise of the Teenage Mutant Ninja Turtles. He is a Yōkai from the Hidden City who befriends April O'Neil and the Mad Dogs and comes to live with April as her new pet.
Mayhem is a dog-like creature with golden-yellow fur as a base color, blue fur on the top of its head, back and tip of its bushy tail (with the latter two being in a flame-like design). It has a jagged red fur-line on the top of its head, as well as the same red color around its red-brown eyes, resembling eyelashes.
Mayhem also has a red nose, a red fur patch around its neck, pointed ears (much like a cat), sharp claws, and sharp teeth with two fangs curving out, similar to a traditional Eastern dragon.
Mayhem has the mystic ability to teleport himself at will, bringing selected other people and objects with him.
- April O'Neil: April rescued Mayhem from Baron Draxum, and he now lives with her as a pet. The two of them apparently have a deep bond. Since Mayhem does not appear at all in the second season, it is not known if he still lives with April after the events of "End Game".
- Council of Heads: Mayhem works as an agent of the Council of Heads, known to them as Agent 64, and was tasked by them with surveilling Baron Draxum's suspicious activities.
- Mad Dogs:
- Raphael: Mayhem has a recurring habit of scratching up Raph's face, despite the fact that Raph usually tries to be nice to him. In one instance, Raph saved Mayhem when the latter was trapped in April's bathroom mirror, and Raph's face was still clawed by Mayhem.
- Splinter: Mayhem once teleported Splinter to safety after he had been seriously injured.
- Baron Draxum: The Council of Heads had suspected Draxum of committing very serious crimes, and they sent Agent 64 to surveil him. The agent stole a mysterious vial from Draxum's laboratory, and it was his escape from Draxum's guardsmen that led to the agent's encounter with April and the Mad Dogs, and him earning his new name "Mayhem," and he continued to investigate Draxum, but now usually accompanied and aided by his new friends. Mayhem's investigation would ultimately lead to the Council of Heads trying and convicting Draxum in absentia for multiple serious crimes against Hidden City law. Mayhem does not appear at all in the second season, so is not shown interacting with Draxum after the latter's exile to the surface world.
- Ghostbear: Mayhem helped April and the Mad Dogs defeat Ghostbear during their clash with him in Bronx Park.
- Mayhem is named after show writer Russ Carney's pet cat.
- It is revealed in "End Game" that Mayhem is an agent working for the Council of Heads.