Invisibility (Q2)

"The invisibility makes you much more difficult to see, though not impossible to see."

- The Quake II Manual

In Nintendo 64 version of Quake II, Invisibility makes the player invisible except for his eyes, lasts for 30 seconds, and in multiplayer respawns after 5 minutes. The effects will also immediately wear off at the end of a level. It can be useful for getting the edge on a target, but remember that other players can still see your eyes! Note that it is rather difficult to see the eyes, especially when the player isn't moving or is in the air. During that time, a grey glow will envelop you, alerting others to your position.

Single Player
As stated earlier, the item can be useful for sneaking up on a target, but excels for ambushes. In Single Player, Strogg monsters will typically not see you unless you attack them. Even brushing by them usually won't make them notice you, and in addition, you automatically put your weapons away while you are using it. One strategy is to move as far through the level and pass by as many enemies as possible, picking up keys, opening locked doors, gathering supplies, and maybe even finishing the level.

Of course, the challenge here is to make sure to find a relatively safe place to be when the powerup wears off. If you want to, you can then backtrack and attack the monsters you passed from behind, as they are usually surprised and more easily dispatched that way. It's also useful for escaping, simply rocket jump to another area if you're caught, and your enemy should lose track of you.

Trivia

 * While the eyes of the player under the effects of this powerup remain visible mostly due to gameplay and balance reasons, this also adds some realism to the game. The human eye works by refracting light through itself, however if it becomes completely transparent (invisible), it will not be able to refract anymore and thus the wearer of the ring would be completely blind.
 * Invisibility therefore works somewhat differently and more effectively than Doom's Blur Artifact. Which reduces player's visibility to a shade and accuracy of enemy attacks instead of eliminating player's bodyframe from plain sight and is therefore unsuitable for sneaking through levels. Upon close contact enemies will notice you eventually, unlike Q2's invisibility.