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 are a rare spawn and 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).