New Playable Character: Wind Waker Link. He's awesome in every way, whether it be persona, weapons, cartoony-ness, originality, or just sheer "WTF I GOT PWN'D BY A LOONEY TOON D:" factor. He's in, naysayers be ****ed.
Kicked out for good: Hmm...That's hard...What character deserves to NEVER EVER be apart of the Smash Bros. universe? Who is SO unpopular in the world that their very name causes an uproar of hatred from within? Who has wronged not only Nintendo, but Gaming in general, with their antics of pure spite? I seriously have no idea who deserves the unflattering title of "Banned from Brawl", who has single handedly dug their own grave, more than...I don't know.
Assist Trophy: a tie between the Elite Beat Agents and Professor Oak. The Prof would send out a Pokemon, at random from Tauros, Pinsir, Typhlosion, Xatu, or Absol, to attack your enemies in various ways. The Elite Beat Agents would dance to motivate you and give you 20% more attack power, and cannot be knocked back (They fit more, I think. C'mon. Their MOTIVATIONAL DANCERS. That positively begs for AT treatment).