Hold RIGHT and then press X, B, B, B, X, B, Y, A.
Hold RIGHT and then press X, X, Y, Y, B, B, B, A.
Play as Skeleton Zeke:
To play as Skeleton Zeke, press and hold down the following button combos when the game's "legal screen" appears (the one with all the copyrights, etc): A, B, X, Y.
While playing a game, hold Right, then press B(2), X, Y(2), X, B, A.