Voltaic Guardian
Voltaic Guardians can only be found in maps and have the same model as Flame Sentinel but use lightning skills instead of fire.
They rarely spawn but are known to spawn in the following maps:
Overgrown Ruin (66), Sewer (67), Cemetery (67), Wharf (67),Vaal Pyramid (68), Museum (68), Catacomb(69), Promenade (69), Villa (70), Temple (71).