Ghostliness

Very specific opponents are incorporeal beings such as various wraiths, ghosts, clouds of mist or water and air elementals. Since these beings have no material substance, ordinary weapons cannot wound them at all and pass through them as through the surrounding air.

How to fight them

Against these creatures there are specially enchanted weapons (Spiritual Weapon, Ghostliness, Destroyer of Magical Monsters); others are pointless. You can defend against them with a strongly enchanted weapon (Destroyer of Magical Monsters), a shield or armor (Protector against Specters).

If you do not have such a weapon, you cannot threaten a wraith in any way nor defend against it with a weapon (only dodge, i.e. use unarmed defense).

No armor and no penetration

Spectral attacks do not overcome armor at all and have no penetration (and the reverse also applies). After a successful hit they therefore do not roll for penetration, but wound directly. Likewise, if someone has a weapon against wraiths and hits, their penetration does not matter at all (the wraith is incorporeal and strength is not important at all).

Armor intended for fighting a spectral opponent only reduces the damage (for example by half), but never stops it completely.