To get secret Chainsaw weapon, pause the game and press Up, Down, Up, Down, Left, Right, Left, Right, Z, Nunchuck Down, Z, Nunchuck Down.
To get secret Baby Rattle weapon, complete the game on the Easy difficulty setting. Then, pause the game and press Left(2), Right(2), Z, Nunchuck Down(2), Z, Up, Down.
To get secret Telephone weapon, complete the game on the Normal difficulty setting. Then, pause the game and press Right, Left, Right, Left, Down(2), Up(2), Z, Nunchuck Down, Z(2), Nunchuck Down(2).
To get secret Swordfish weapon, complete the game on the Hard difficulty setting. Then, pause the game and press Up(2), Down(2), Left, Right, Left, Right, Z, Nunchuck Down, Z, Nunchuck Down.