Unlock all Extras

At the chapter select screen, hold +, and press Right, Right, Left, Left, 2, 2.

NOTE: Imput code quickly.

Glitches

Normally, you're only supposed to hold 6 grenades but when you have a grenade thrown at you you can pick it up and throw it again. Instead of throwing it you can keep it for later by pressing the minus button a second time after picking up a grenade. There's no limitation of grenades when doing this.