Rampage World Tour
At the Options menu, hold Select and press Up, Down, Left, Right, Down, Up. The 'Players 1 or 2' option will be unlocked. Now you can play a two player game with two linked Game Boys.
Play as Tiny:
Select Ralph as a character, then die. Now quickly press Select, A, B, B, Up, Down, Forward, Back after transforming into a person.