Body Harvest 

All weapons 
Enter "ICHEAT" as a name. Then while playing a game, press A, Right, C-Down, C-Right, C-Up, A, Left.

Weapons power-up 
Enter "ICHEAT" as a name. Then while playing a game, press C-Down, C-Up, Up, Z(2), Left, C-Right.

Smart bomb 
Enter "ICHEAT" as a name. Then, press A, C-Up, C-Up, Up, Left.

Restore health and fuel 
Enter "ICHEAT" as a name. Then while playing a game, press Down, Up, Right, A, B, Left, C-Right.

All artifacts 
Enter "ICHEAT" as a name. Then while playing a game, press Up, C-Down, C-Right, Z, Up, Left.

Weak Boss 
Enter "ICHEAT" as a name. Then while playing a game, press Z, C-Right, C-Right, B, Left, C-Right.

Kill Adam 
Enter "ICHEAT" as a name. Then while playing a game, press B, Left, C-Right, C-Right, Down.

Black Adam 
Enter "ICHEAT" as a name. Then while playing a game, press C-Left, C-Right, A, C-Down, C-Right, Left.

Tall Adam 
Enter "ICHEAT" as a name. Then while playing a game, press B, A, C-Up, A, C-Up, A.

Short Adam 
Enter "ICHEAT" as a name. Then while playing a game, press Down, C-Left, A, Right, Z.

Mutant alien 
Enter "ICHEAT" as a name. Then while playing a game, press C-Down, Up, Z(2), C-Right, Right.
Enabling this cheat while facing a harvester will transform that alien into a mutant. Repeat the code to disable it.

Fat legged aliens 
Enter "ICHEAT" as a name. Then while playing a game, press Left, A, Right, Down. 
Repeat the code to disable it.

Dancer 
Enter "ICHEAT" as a name. Then while playing a game, press Down, Up, C-Up, Down, C-Right, C-Right.

Surreal mode 
Enter "ICHEAT" as a name. Then while playing a game, press C-Down, Up, Right(2), C-Right, A, Left
to make the buildings jump. Repeat the code to disable it.

Additional difficulty levels 
At the difficulty selection screen, repeatedly press Left to access the "Very 
Easy" setting or repeatedly press Right to access the "Very Hard" setting.