[Powder]

I have to admit, I've always been a sucker for this concept in general. Like when Bowser teams up with Mario & the gang.

One of the coolest concepts in TMNT history (IMO) ties into this, the episode of Next Mutation where Shredder, now a broken homeless man, is pitied/taken in by Splinter. He turns on him in the end, but there was a lot of potential in that story, & it's especially neat if you think of it as being connected to the live action movies.