Cheat:

 These codes are entered at the screen where you choose the fighter.
 These have to be done quickly, like doing a special move. If it
 works, it'll make a noise.

 Allows you (and your opponent) to rip limb from body:

 U+L, U, D, D+R  (W+A, W, S, S+D on keys for Player 1)

 Gives you unlimited continues:

 U, D, U, D, U, D, L, R, L   (W, S, W, S, W, S, A, D, A  on keys for
 Player 1)

 Fight as BOSSES:

 Schrapp:   Highlight Psyclopps and hit PK, PP, SK, PP  (J, I, L, I on
            keys)
 Carnigore: Highlight Master Pain and hit SK, PP, PK  (L, I, J on
            keys)

FunCheat:

 Turn your fighting game into a disco dancing game with this secret
 code. From the fighter selection screen, press [W],[S] and then [J]
 and [L] simultaneously on the keyboard. You'll hear an explosion if
 this key sequence is entered correctly.
 Next, press [Esc] to clear your fighter selections. Now, choose any
 two fighters and you will be brought to the hidden disco arena where
 you and your opponent can dance the light fantastic!