As the original versions of Mickey Mouse finally entered the public domain, he and the other characters depicted in the "Steamboat Willie" short are now available to be used for any purpose, both commercial and non-commercial, without worrying about any strikes or legal issues. Since this is the case, perhaps he can be included as a character in Mushroom Kingdom Fusion?. He's not synonymous with video games, but he has been in a number of them. Sega's Illusion series, Kingdom Hearts, and especially "Mickey Mania" which features a Steamboat Willie level. I think it would be cool to play as a character that isn't tied to any one company any more, and without fear of being taken down (unlike Nintendo's IPs)
The only caveat is: he can only be in black and white, and for now it's best to refrain from referring to him as "Mickey Mouse". Until further shorts enter the public domain in the coming years.