Some TMNT stuff really isn't for little kids.
Waylon Jones, also known as Killer Croc, is a criminal with a reptilian appearance triggered by advanced regressive atavism. Despite his "Killer Croc" moniker, he is not in any way actually crocodilian.
Killer Croc and a group of mercenaries were traveling through the sewers of Gotham. Croc's plan was to steal Batman's car, the Batmobile, scrap it and sell its parts on the black market. He and his thugs stumbled upon a temporary hideout the reality-displaced Turtles had set up in the Gotham sewer system. Noticing the amount of teen related items, such as Michelangelo's favorite video game and still warm pizza, Croc assumed the place belonged to a group of harmless kids and taunted his prey to stop hiding and make it easier on themselves, smashing the video game to pieces as an example which upset Mikey. The Turtles promptly sprang into action, and Croc and his men were easily defeated by the four ninja brothers.
- Croc is one of the few mutants that any version of the Turtles have encountered whose mutation has nothing to do with mutagen, as that substance quickly loses its effectiveness in the DC Universe.