Ancient of vitality
An ancient of vitality inhales death and exhales life (while this might sound like a great attack to be hit by, it's really, really not).
"Flakes of black ash rise around you."
The inhalation affects one valid target within 4 squares of the ancient at random. A target must have at least one organic item in open inventory.
The ancient attempts to consume the "death" of one organic item per 3 levels (5 items for a typical ancient). An item whose "death" is consumed fills with biting larvae, and may totally disintegrate (destroying the item and spawning strange larvae in the process). Stackable items are immediately consumed, while other items gain a level of larvae-infestation. Worn or wielded infested items bite the wearer each turn. If an item exceeds three levels of larvae infestation it disintegrates. Larvae-infested items gradually die again, losing one level of infestation every 10-18 turns.
(Note: a destroyed container will drop its contents on your square)
"Waves of light roll from the ancient of vitality's petals!"
The exhalation overloads one living target within 8 squares with corrupt life energy. The target loses one level per item's "death" that was consumed by the inhalation. Each level lost transforms into a beauteous one that spawns adjacent to the target.
An ancient of vitality poses a critical threat to the typical ascension kit. When facing an ancient of vitality it's best to immediately use an escape item and stash all organic items in a safe place before returning. As an added benefit, depriving the ancient of organic items to destroy also deprives it of its level-draining exhalation. However, since unicorn horns are organic, great care must be take to avoid dying of illness from the ancient's melee attacks. Crucially, dragon scale items are sufficiently inorganic to evade the ancients inhalation attack, so they may be used to great effect.
dNetHack ancients are very loosely based on D&D Ancient Baatorians. Only two examples of ancient baatorians were actually encountered during the period in which they were introduced: a nupperibo with constitution-draining tentacles (stated to be a metamorphosing, larval baatorian) and a shapeless thing that inhales light/reflectivity and life and exhales darkness. There were also said to be spined creatures frozen deep under the ice in Cania. A later source claimed that Zargon was another ancient baatorian, but Zargon originated over a decade before the later idea of ancient baatorians (and over two decades before the source tying them together) and is obviously unrelated.