Ghosts (Heretic)

Some monsters in Heretic (Golems and Undead Warriors) can appear in a form of a ghost. Ghosts are translucent and cannot be harmed by certain weapons, which are defined as non-magical weapons. 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.

Ghosts cannot be hit by the following attacks:
 * Staff - Either mode
 * Ethereal Crossbow - Small bolts
 * Phoenix Rod - Normal fireball (however, splash damage will hit them)
 * Firemace - Either mode
 * Undead Warrior's throwing axes (either type)