An insectile devil, fighting with a spear and utilizing cold attacks, from the Nine Hells of Baator. They are the most alien of the Baatezu, having mental processes humanoids would consider insane. The tieflings they produce, kept in insane asylums by humans, pass as sane to gelugons.
I think the summoning abilities of devils should be reconsidered. Starting with a single gelugon, my party eventually had to fight off 3 gelugons, 8 osyluths, and however many lemures they all felt like summoning.