A tattered black cowl obscures the spectral monk's face. Given the burning green eyes and foul stench he exudes, perhaps that is for the best. Tattered rags cloak his shimmering pellucid form. Its ghostly body flickers in and out of existance, as if only his desire to destroy keeps him bound to this plane.
They have the ability to heal themselves and the monastic liches, so you may want to kill them first. The upper level of the monastery is somewhat more dangerous than the lower level because of them. The spectral monks are actually more likely to hit you with warding spells.
Spectral monks disperse into the wind almost immediately once dead. So it is best to search them immediately after killing. They will decay at the start of what would have been their next round to perform an action.
When they kill you they will sometimes claw into your forehead, which gives a rank 3 head wound and nerve damage:
The spectral monk moans victoriously!
A spectral monk's eyes blaze with hate.
A spectral monk claws an unholy symbol into your forehead!
A spectral monk pulls back his cowl a moment revealing nothing but a pair of blazing green eyes floating in the dark emptiness.
A spectral monk shimmers with an eerie green light.
Behind the scenes
It is difficult to parse much of any symbolic or intentional allusions out of The Monastery, but it is possible the rare messaging the monks perform when you are dead refers to "The Masque of the Red Death". It is set inside a sealed abbey as a plague sweeps the outside world, here the Wars of Dominion, while the nobles inside ignore their surroundings and hold masquerades with grotesque exaggerations of faces. (This would reflect the emotive faces in the lower level and the noblewoman statue. It is worth noting the masquerade rooms are spoken of as dreams.) When an attendee dressed as a victim of the Red Death appears in the abbey, they discover to their horror there is nothing beneath its robes and everyone dies. In the story it is attacked with a dagger. While the spectral monks mostly carry black modwir staffs now, in the I.C.E. Age their weapon was daggers.