Until I can figure out what to do now that nick vs smash is canceled I’ll give you some concepts and trivia.
1. April vs Peach is the first canonical matchup. The plot goes that the Krang was gonna travel to other universes to conquer and grab things that could stop the tmnt, however April was eavesdropping on them and was trying to stop them and went to attempt to sabotage them but failed she was then thrown into a portal ending up in the mushroom kingdom and fell on Peach’s Freshly-Baked Cake
2. Leo was originally gonna fight Marth but was changed over to Fox once I realized that they had more in common.
3. I didn’t want two universes fight each other twice. Though Rugrats and Wild Thornberries might be from the same universe not sure.
4. Certain battles played out in different styles in my head, Peach vs April was a motion comic, Aang vs Link was Stop Motion, Fox vs Leo looked similar to the arcade beat-em up games, Marth vs Mikey in Fire Emblem Heroes Style and Pikachu and Pichu vs Ren and Stimpy in the Style of the Pokémon Anime.
5. Each portal had a different style depending on the universe it was headed to, the Mario portal would have been pink and yellow reminiscent of Partners in Time and Danny Phantom would’ve been a ghost zone portal.
6. I made some mock-up matches for a Round 2, one of which was Avatar Aang vs Fierce Deity Link.