Play as Shaq:
Highlight Survival then press Lleft, Left, Left, Left, Right, Right, Left, Left, Right, L + R.

Play as Michael Jackson:
Highlight Arcade then press left, left, right, right, left, right, L plus R.

Play as Rumbleman:
Highlight Championship and press Left, Left, Right, Left, Right, Right, Left, Right, Left, and L+R.

Thanks to Revolution reader Andrew Chien!