Note: For all map points of nameds in Miragul's Nightmare (for "miragulmare.txt" map files), see this quest entry.
Gilibus the Unseen spawns in the castle (bottom floor, back room with the bookcases). PHs are the "an unseen warrior" mobs in this area.
He hits for a max ~13,500. Be very careful as he casts a strong, short-duration damage shield on himself.