Invisibility is a power, limited ability, an item or a power up that can make objects or characters completely unseen or partially invisible. Often while attacking or moving, noises and projectiles players launch can cause the player to become visible. In some games, invisibility is a stealth bonus that allows critical strikes. However, invisibility does not always mean players are undetectable by enemies, who sometimes come equipped with sensors.
In some games, invisibility sometimes equates to temporary invincibility or is a glitch that can be exploited to advance past enemies and stages that would be more difficult while visible.
The Power Up
Some items can turn the player invisible when used and expire within a limited time frame. They often can be stored for later use or, in the case of some items, turned on or off as needed. Notable examples include the stealth boy from the Fallout series and the active camouflage from the Metal Gear Solid series.
Invisibility is sometimes given as an ability or spell, usually with a mana/energy bar dictating its length of use. In these cases, the strength and duration of the spell is often determined by player level and can be affected by equipment worn. Notable examples include the illusion spells from Oblivion and the Arbiter's cloaking ability from Halo 3.
Stealth without Items or Abilities
Invisibility can also serve as a gameplay mechanic without items or abilities, often requiring the player to stay crouched or in dark areas to avoid detection by enemies. In these cases, running speed may impact detection, as well as the level of darkness the player is standing in. In many first person shooting games, invisibility on radars can be achieved by not firing weapons or with a related perk. Notable examples include the stealth found in the Splinter Cell series and the ghost perk from the Call of Duty series.
Some games require players to detect hidden enemies. This can be done with sensors, abilities, or other items. In other games, invisibility can be limited to specific units or races, and can be countered appropriately by others. Notable examples include the detectors in the Starcraft series and the various detecting abilities and items found in World of Warcraft.