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In addition to weapons, you need to find powerups to assist you in defeating the monsters. You might also need to find switches and/or keys to finish a level.

[edit] Powerups

Powerup	Effect	Duration
Bullets, Shells, Rockets, Plasma Cells	Ammunition for weapons
Health potion, Stimpack, Medikit, Soul sphere	1%, 10%, 25%, and 100% health boosts, respectively (only health potions and soul spheres will boost health above 100%)	Instant
Spiritual armor, Security armor, Combat armor	1%, 100%, and 200% armor boosts, respectively (security armor will not boost the player to over 100%)	Instant
Megasphere (Doom II series only)	Boosts both health and armor to maximum (200%)	Instant
Radiation suit	Protects against damaging floors. (Some floors can still damage if you stand still on them.)	60 seconds
Berserk pack	Makes fists ten times more powerful, heals player to 100% health if lower upon pickup	Level
Backpack	Doubles ammo carrying capacity (only first picked up) and provides some ammo	Episode¹
Computer map	Reveals unexplored areas on in-game map	Level
Key	Opens corresponding locked doors; comes in keycard or skull form	Level
Light amplification visor	Renders dark areas at full brightness	120 seconds
Partial invisibility	Makes player difficult to see; makes monster aim less accurate	60 seconds
Invulnerability	Provides immunity to damage, player's view (except for sky) becomes extremely bright	30 seconds

1. Doom II is not divided into episodes; the backpack's effect lasts until the end of the game

[edit] References

• Weapon power: Doom Weapon Damage Information by George Bell
• The Creatures: Doom and Doom 2 Creature Information