I mean, Sandy's stage is Glove World (you'd think that'd be Patrick's.) instead of the Tree Dome. So the Omashu stage could be either Toph or Zuko. Hell, even Azula since her and Aang had a pretty flashy fight scene there. I'm not really sure which of the 3 TMNT characters get which stage, any combination works well. I think the Rooftop stage is Leo's cause is file name was "Moon", but that's a guess.
If the game has DLC, I imagine some characters like Zuko/Toph(depending on who doesn't get in), Raph, Donnie, Shredder ect. would be good for those two series, since those are the two I give the most of a ** about. But outside of that El Tigre or Jenny would be cool. One's a superhero the other's a Robot. **** would pay big money for Squidward and Mr.Krabs tho.
Can I say how weird and dank it is to be talking even remotely seriously about a Nick fighting game?
Rocko would be fun, but he might be too chill like Arnold.