Partial invisibility effect (also known as the fuzz effect) is a visual effect which is used in Doom for Spectres and for the Partial invisibility player powerup, though replaced by true or table-based translucency in some source ports. The engine is technically capable of applying the effect to any arbitrary thing, but by default it is only used for the aforementioned. Heretic, Hexen and Strife do not use this effect at all.