Enter the following codes while the game is paused:
World's Most Interesting Bomb: Press Down, Right, p, p, Left, Left, Up, l, g.
Thumper Weapon: Press Down, Up, Left, Left, g, Up, Right, Down.
Twister Weapon: Press Down, L1, l, g, Right, Up, u.
Hand Grenade: Press g, p, l, l, L1, Right.
Bones Airstrike: Press Down, Up, p, Down, Up, Down, L1.
Super Chain Gun: Press Left, L1, Down, l, g, Up, Down.
Sniper Grenade: Press Up, l, L1, Left, p, g, l.
Mortar: Press Left, L1, g, l, Right, p, Left, Left.
Level Select
At the title screen, press Left, Cir, Tri, Up, Square to make a level-select option appear.