Partial invisibility effect

Partial invisibility is a visual effect which affects certain monsters, and the player when he picks up a blur artifact. Although the game algorithm allows any object to be partially invisible, in official game play the spectre is the only invisible thing other than the player. The concerned thing retains its shape, but instead of color we see black pixels scattered randomly (applied by colormapping the pixels behind it to darker shades), which makes the object more difficult to see.

When the player is in such a status, the monsters' behaviour changes. They can still spot and assault him, but both projectiles and melee attacks will be badly aimed, and will be scattered on a large firing angle, thus reducing the possibility the player being hit. Against monsters which throw fireballs, this means it is better to remain still rather than dodging as usual; dodging may cause the player to blunder into a projectile.

In Heretic, Hexen, and some source ports, partial invisibility is achieved by translucency (using the TINTTAB color map). Heretic and Hexen feature several invisible or "ghost" monsters.