Enter these following cheats in the Cheat menu!
THSSLKSCL = god mode
CMGTSMMGGTS = all weapons
BLLTSRRFRND = unlimited weapons
FRTHSTHTTRLSCK = infinite lives
RBNSMITH = big heads, invincibility, all weapons, unlimited ammo, and creditsSNFFRR = disco mode
DLKTDR = wireframe mode
THBST = gallery
FDTHMGS = credits