Use the following combos at the title screen (you can input them with the controller in the 1st port) and press start then:
Unlimited Ammo: Black, White, L, R, right-thum, right-thum, Y, X
Unlimited turbo: d-pad up, d-pad up, d-pad down, d-pad down, d-pad left, d-pad right, d-pad left, d-pad right, B, A
Get All Battle Modes: Y, A, X, B, click Left Analog-stick, click Right Analog-stick, Black, White, R, R
Get All Arenas, Multiplayer Boats and Battle Modes: X, Y, Up, Right, Left, Down, Up, Down, L, L