All special items
Stand on the mushroom to face the scientist when first meeting him. Then, quickly press R(2), Analog-stick Up, Analog-stick Down, Up, Down, C-Up, C-Down, C-Left, C-Right, C-Up(2), C-Left(2), C-Right(2), C-Up(2), C-Down(2), Analog-stick Up, Analog-stick Down, Analog-stick Left, Analog-stick Right, Start to receive all special items.

Final battle
Pause the game, then press A, B, A, B, A, Left, Right, Up, Down, Z to advance to the final battle with Grgh the Hellish.