Some monsters in Heretic (Golems and Undead Warriors) can appear in a form of a ghost. These have the GHOST thing flag, which makes them translucent and not hittable by certain attacks, which are defined as non-magical. Projectiles that cannot hit ghosts will simply travel through them as if nothing was there. Additionally, the Disciple of D'Sparil seems to possess the ability to flicker in and out of tangibility when preparing its attack, so a player might find a couple of their crossbow bolts going right through them. They can be harmed by other attacks, such as: