At the Title screen, press L, Select, A, Select, R, A, L, Select. Press Select and R or L to scroll through the levels. Press Left to make the boomerang appear around the word Start.
All weapons
At the title screen, press L, Select, A, Select, R, A, L, Select. Start a game, hold Select and press B.
Fly mode
At the title screen, press L, Select, A, Select, R, A, L, Select. Start a game, hold Select and press Up, Down, Left or Right.
Unlock the Lakamul Rain Forest level
At the title screen, press A, L, A, R, A, L, Select, Select, Start.
Nine continues
Quickly and repeatedly press Start at the continue screen until the remaining number of continues increases to nine. Alternately, intentionally lose all your lives during game play in level 1, then press B(3) at the continue screen.
Free movement
Enable the "Master code", then begin game play on any level. Hold Select and press the D-pad during game play to move in any direction.