I wasn't really allowed to watch cartoon as a kid, so on the off chance I got to watch TMNT at a friend's house, the stuff I did get to see has stuck with me. I have a distinct memory of a character who had the ability to transform into anyone he saw, Skrull-style. He had these tubes coming out of his back with sludge or something running through them. He had a run-in with Rocksteady I believe, who pulled some of his tubes out and made him start spraying everywhere, making him scream in distress as Rocksteady walked away. The turtles saw him and shoved his tubes back in, and they became friends. I have another memory of this character seeing an old lady and transforming into a copy of her.

Is this a real episode and a real character or some weird fever dream I had? Wikipedia is being no help right now, thanks.