All Monsters (3)

• Invisible Stalker - Creatures native to the Elemental Plane of Air that serve wizards and sorcerers
  BFRPG, OSE, OSRIC
• Poltergeist - Non-corporeal invisible spirits of humans who died tragically or were murdered
  OSRIC
• Spectral Troll - Invisible creatures created from merging troll and extra-planar essences
  OSRIC