Lately I've been really tickled by the idea of a "fangame" that uses original designs and can be sold without legal issues. From that idea these four friends were born: Spritey, Snuckles, Ed, and The Princess.
In theory this would be a Paper Mario-style RPG where you meet your partners in legally-distinct worlds. You might meet Snuckles in a "Verdant Hilly Zone", or the Princess in a "Kingdom that has many vegetables including but not limited to Mushrooms". Ed is from Pocketmania, that's a gimme. Of course the words Sonic, Mario, and Pokemon would appear nowhere in the game or branding. No idea how this would actually work out in terms of C&D notices, but it sure would be fun to try.
The sprites themselves are pretty similar to PM64, but they're 8-bit. I think 8-bit sprites against a 3D world with some amount of dynamic shading would make for some pretty cool contrast.
I exported Ed's arm 1px too high but I'm too lazy to fix it (doesn't bode well for my ability to complete an entire game)