Monster Manual 5.5e
Ghast gravecallers wield fell magic and converse with corpses. They might pose as liches or vampires.
Ghasts
Tyrants among Corpses
Habitat: Swamp, Underdark, Urban; Treasure: Any
Ghasts are reeking, undying corpses closely related to ghouls. They hunger for the vices they enjoyed in life as much as they do for rotting flesh.