Repeated press Left at the difficulty selection screen to access the "Very Easy" setting or repeatedly press Right to access the "Very Hard" setting.
Fat legged aliens
Enter ICHEAT as a name. Then, press Left, A, Right, Down during game play.
Mutant alien
Enter ICHEAT as a name. Then, press C-Down, Up, Z(2), C-Right, Right during game play. Enabling this cheat while facing a harvester will transform turn that alien into a mutant.
Surreal graphics
Enter ICHEAT as a name. Then, press Down, Up, Right(3), A, Left during game play.
Weapons power-up
Enter ICHEAT as a name. Then, press Down, Up(2), Z(2), Left, Right during game play.
All weapons
Enter ICHEAT as a name. Then, press A, Right, C-Down, C-Right, C-Up, A, Left during game play.
Dancer
Enter "ICHEAT" as a name. Then while playing a game, press Down, Up, C-Up, Down, C-Right, C-Right.
Suffer mode
Enter "ICHEAT" as a name. Then while playing a game, press C-Down, Up, Z(2), C-Right(2). Repeat the code to disable it
Smart Bomb
Enter your name as ICHEAT, during the game press A, C-Up, C-Up, Up+Left to launch a smart bomb. The bomb will destroy all minor enemies, shield generators and processors on the screen.