Enable the console in the game options, and enter the following commands to enable their effects.

Effect	Code
Asbestos Armor	burnme
Bazooka	vanilla
Bulletproof Armor	shootme
Dark Staff	kesofdeath
Dog Mode	cujo
Drunk Missile	booze
Elasto Mode	boing
Enable Cheats	dipstick
Excalibat	homerun
Firebomb	firebomb
Flamewall	bones
God Hand	seeya
Heat Seeker	hottimes
Infinite ammo	gunfinity
Invincibility	god
Invincibility, Infinite ammo, and an Excalibat	chojin
Mercury Mode	flyboy
MP40	plugem
Shrooms Mode	badtrip
Split Missle	splitem