Body Harvest cheats and cheat codes for Nintendo 64

Enter "ICHEAT" as a name. Then during game play hit the 
following button combinations:

Change Adam to black: C-Left, C-Right, A, C-Down, C-Right, Left.

Dancer: Down, Up, C-Up, Down, C-Right, C-Right.

Fat aliens: Left, A, Right, Down. Repeat the code to disable it.

Get smart bomb: A, C-Up, C-Up, Up, Left.

Get weapons power-up: C-Down, C-Up, Up, Z, Z, Left, C-Right.

Kill Adam: B, Left, C-Right, C-Right, Down.

Mutant alien: C-Down, Up, Z, Z, C-Right, Right. 

Refill health and fuel: Down, Up, Right, A, B, Left, C-Right.

Change Adam to short: Down, C-Left, A, Right, Z.

Surreal mode: C-Down, Up, Right, Right, C-Right, A, Left

Change Adam to tall: B, A, C-Up, A, C-Up, A.

Unlock artifacts: Up, C-Down, C-Right, Z, Up, Left.

Unlock weapons: A, Right, C-Down, C-Right, C-Up, A, Left.

Weak Boss: Z,C-Right, C-Right, B, Left, C-Right.

More difficulty settings:
Go to difficulty selection menu, press Left several time
to change the difficulty to "Very Easy" or press Right several times 
to change to "Very Hard" setting.