Ancient of death
Its weapon attacks are high-damage and can drain levels and even behead its target. When destroyed it explodes, dealing physical damage. It has a very low AC, and thus can be very hard to hit.
Unlike most other demons, ancients of death will summon groups of nupperibos instead of additional major demons. However, this does not apply when self-polymorphed into one, making that an easy way to get a tame ancient of death.
Ancients of death breath in life and breath out death. If a living (ie, not undead or a golem or other nonliving creature) target is within 4 squares of an ancient of death, the ancient will suck some life out of it, dealing level/3 d4 damage (ie, between 5d4 and 10d4). After inhaling life, if one or more targets that are sensitive to death magic are within 8 squares, the ancient will exhale death at one such target. Hostile ancients will target the player character with high priority, unless the character is 100% immune to death magic (death spells are able to partially penetrate magic resistance, dealing 4d4 damage). If the character is not a valid target, the ancient will choose the closest valid target instead.
Tame ancients of death make powerful pets, in large part due to the rarity of targets able to resist their breath. Ancients can reach a maximum of 30th level.
At most 4 ancients of death will appear per game.