Originally posted by TheCountAlucard
Ghosts aren't immaterial in the Underworld, thus they aren't immaterial in shadowlands at night. At least in 1e, you had to be immaterial to use Arcanoi to possess a corpse or living body, so any effect that rendered you material would also shunt you out of a body you were inhabiting.
Basically, you could replace my question with, "Does a nemissary have to be dematerialized to possess a corpse?"
Probably not? I don't want to tie our hands regarding the specific mechanics of dematerialization vis-a-vis spiritual realms and/or possession; I just think that nemissaries having to ditch their bodies "at the door" is kind of silly and to be avoided. Exactly how that'll dovetail with broader systems and interactions is up in the air.