Ghosts
The Lyssa purple apes sometimes look like purple ape illusions, sometimes like real living-dead apes. I find that the ghostlike effect of Grenth’s unnamed effect needed to damage shades while attacking the priest of Grenth, the ghostlike appearance goes away if I use stealth. Perhaps other visual effects also clear the ghost visual effect.
//Portable Corpse
(I want to make a joke here about being a corpse and not a ghost, but fear that someone might misread it as being part of the bug report)