If I was making a Mario game, a multiplayer spin-off specifically, I'd only do it if Ninty gave me free range over characters from Mario's entire history (excluding characters owned by outside sources like Geno and Oogtar) - otherwise I'd just go to Activision or Sega and say "hey, you wanna put Crash/Sonic in this?"
I think I could work with mandates for a platformer though.
I think I could work with mandates for a platformer though.