Play as Robert the Robot
     Beat  the game first, then beat everybody again in Faster mode in
less than one minute.

Play as the Joker
     Beat the game first, then beat all 100 characters in survival mode.

Play as the Master
     Beat everyone in Master Challenge mode.

Play as Ushi the Cow
     Beat  the  game  first, then in Rodeo mode, survive with Ushi for
one minute. Make sure you don't kill Ushi.