Pause the game and press Up, Down, Left, Right, Select. Repeat the code to turn the inertia on and off. With inertia on, the sub coasts a little bit before stopping. With it off, the sub can stop on a dime.
Slow Motion
Pause the game and press Up, Down, Left, Right, Up, Down, Left, Right, Up, Down, Left, Right, A, B, B and A. Perform the code to toggle between normal and slow speeds.
Level Skip
Pause a game, and press A, B, Select, Right, Left, Left, Right, Select, B, A, B, B and A. You can do this once per game.
99 Subs
As soon as your number of subs reaches "0," pause the game and do the Level Skip code. This starts you with 99 subs. You can do this once per game.
Full Systems
Pause the game and press A, B, Select, A, B, Select, A, B, Select, A, B, Select, A, B, Select, A, B, B and A. You can do this once per game.
Double Scoring
Pause the game and press A, B, B, A, Right, Down, Up, Left, Left.
No Forced Scrolling
Pause the game and press Up, Up, Down, Down, Left, Left, Right and Right. This allows you to turn the scrolling movement on and off.