Astral

Astral weapons command powerful spiritual energy from the Astral Plane. This rune has the same effects as a Ghost Touch rune, plus Strikes with it deal an extra 1d6 spirit damage. If used to attack a creature that's possessing another creature, this weapon deals no damage to the possessed creature. On a critical hit against a creature possessing another creature, the possessing creature must succeed at a DC 26 Will save or be expelled and unable to possess a creature for 1d4 rounds.