Big Heads:

During gameplay HOLD BACK and press A, X, B, Y, A . A message will confirm correct code entry.

Chicken Heads:

During gameplay HOLD BACK and press X, X, Y, A, B . A message will confirm correct code entry.

Flat Characters:

During gameplay HOLD BACK and press B, A, X, Y, A . A message will confirm correct code entry.

Helium Mode:

During gameplay HOLD BACK and press X, A, Y, B, X . A message will confirm correct code entry.

Hit A High Note:

During gameplay HOLD BACK and press X, A, Y, B, X . A message will confirm correct code entry.

Slow Motion:

During gameplay HOLD BACK and press Y, Y, B, X, A . A message will confirm correct code entry.

New Character:

Finish the game once and unlock a new character has infinite rocket ammo.

Secret people:

To unlock people with better ratings, beat the X, or bonus objective in each campaign level.