A partial invisibility powerup (called blur sphere or blur artifact in the manuals) is an item that appears as a floating red and blue orb with a pulsing eye-like pattern. Picking one up will grant the player temporary partial invisibility. The player's sprite (as seen by other players in multiplayer mode) will be given a filter similar to that of the spectre, while the affected player will see their own weapon and hands as partially invisible. When 5 seconds remain, the weapon will begin blinking, signaling the end of the artifact's effects; the player's sprite, however, remains filtered until all 60 seconds have expired. Contrary to what most players would think, picking up one partial invisibility powerup while another is still in effect does not render the player invisible for an additional time of 60 seconds, but merely resets the invisibility time to 60 seconds. When the invisible player is killed, their corpse sprite will retain its blurry appearance, similar to that of a spectre's corpse.
Monsters firing upon an affected player will have their accuracy reduced, in that their aim is offset by a random angle, causing them to miss more often. This however may cause more experienced players, accustomed to monsters firing directly forwards, to inadvertently dodge toward incoming projectiles. Nevertheless, a blur sphere confers a definite advantage against long-range hitscan attacks such as those of zombies or spiderdemons. On the other hand, the partial invisibility is unable to disrupt monster melee attacks (though the monsters do appear to spin around in confusion) or arch-vile flames.
In various console ports of Doom, the Partial Invisibility's effect is changed to a slightly translucent/see-through appearance versus the filtered effect seen in the PC version (as such an effect was not possible to be replicated). Despite this, the reduction in monsters' accuracy is still present, except for the Super NES port: when a sphere is picked up, the player will be rendered completely invisible to his enemies' sight and they will not engage him until he attacks. Doing so will give away his position and they will fight him in a regular fashion as if he didn't have the effect in the first place.
Doom 64's Partial Invisibility item's appearance is a dark red sphere with a central core emitting multiple electric shocks. Instead of the filter effect of the PC version, the Marine will appear slightly translucent.
ZDoom based source ports alter the behaviour of the powerup so that as well as the above, unalerted monsters are not alerted when the partially invisible player is within their sight like the similar power up in Quake.
Partial invisibility can also be invoked with the cheat code idbeholdi.
In -altdeath mode, partial invisibility and invulnerability spheres do not respawn. Some fan-made source ports allow flags to be set to allow them to respawn. Also, deathmatch players should remember that weapons with visible projectiles (particularly the plasma gun) can give away a blurred player's position, as the opponent may target the shots' point of origin.
This item is included in the items percentage displayed at the end of each level.
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