Bhut
The Bhut (wut-wut) was one of David "Zeb" Cook's bright ideas for X4-5-10: Desert Nomads series, which (somehow) didn't make the Companion Set as the malfera et al. would. Look for them instead in AC9: Creature Catalog and various Mystara supplements.
Sir Mix-A-Lot cannot lie. But these monsters can.
In daylight they take the form of humans (and can't be sussed out by Expert-level know-alignment!). At night they own their morally-true form: mostly-reptilian, with shaggy hair and claws and fangs (hey, Triassic Park!). Then "they hunt humans and demi-humans for food" (per AC9), in bands of 2-8. Home base is best sited somewhere most humans would be transient... like, oh, beside a mountain pass where Iranian-themed merchants and army camp-followers are going to-and-fro.
They shun most weapons, even in human form, so the monk is a popular cover in-between predation. Instead bhuts use their bite which is numbingly cold, demanding a Paralysis saving-throw. Losing that 'throw costs -2 to-hit rolls and a loss of Initiative for 1-4 rounds.
They share undead immunities: poison, for a start. Where they must take saving-throws, those are at "a level higher than their Hit Dice" usually "7+2**" in Basic Dungeons & Dragons terms.
Here's where Zeb's design got stupid, likely costing this monster its Companion berth: a single hit from a blessed weapon will kill one instantly" Also Zeb never quite figured out where it should live on the vampire/lycanthrope spectrum. All that; and its name, glorious to ten year old gamers for a generation.
The bhut's origin is from the Indo-Aryan bestiary (which might not distinguish undead / demon / lycanthrope very well itself).
Third Edition[edit | edit source]
Nobody much liked Zeb's dumb design, but there were gamers from 2000-on who wanted the bhut done right. That is: as undead.
First Scott Greene floated the "bhuta" in Tome of Horrors. Then in 2003 WotC figured that the Fiend Folio line was still lying on the table and could take this one on. Both bhut-ae are somewhat like a revenant inasmuch as they arise from someone done-dirty in a wilderness, now seeking revenge, perhaps against all the living now.
In 3e official content (thereby) the bhut gets 8d12 hitpoints and is an incorporeal spirit. It hides by possessing a corpse, not always its own; otherwise in this form behaving like Zeb's version. Out of that physical cage it is a "humanoid head" with red eyes on a body of "roiling" smoke. (There's an illustration in the book which doesn't much do this justice.)
Although incorporeal this bhut dislikes to pass through stone, which is in fact a weakness (as with certain div). The FF proceeds that the bhut enjoys resistance against corporeal nonmagical attacks. So... except for, like, obsidian daggers, we guess.