Mimi isn't necessarily a bad choice for a Paper Mario rep, but there are so many better options.
- Paper Mario
- Any of the partners in the original or TTYD game
- Lord Crump
- Rawk Hawk
- Count Bleck
All better options over Mimi. Hell, even Francis would be more enjoable to play as.
But this is a Mimi topic... let's ignore the jewels. Her main power is transformation - she disguises as other characters. She tries to convince other people to follow her way. She does have a spider form, but that's her last resort when she's cornered. I'm not sure how well that would translate into Smash, though...