I was saying I'd just go with the standard jokes/memes that Smash and its' respective series has spawned.
Charizard (whom shall be in his purple colour palette swap): Ridley
Luigi: Green Mario (although I don't think I could have that many letters for a nickname)
Ganondorf: Falcondorf.
But I won't do that, because the hilarity will die after seeing it once.
Also, I personally think it'd be weird to nickname characters like Mario or Kirby, since that's always been their name, so if I bought them, I'd most likely not nickname them. Any Pokémon or avatar character is fair game to be named whatever my heart desires though, since they've always held the ability to be named.
Edit:
If I get Sonic, I'm calling him Sonikku.