It is normally only generated in Gehennom, but is also a valid form for polymorphing, e.g. from a polymorph trap; this makes it a potential nasty surprise for players. Bone devils are also eligible for gating by other major demons.
Bone devils are not particularly threatening to an average player that has reached Gehennom; as the result of a monster stepping on a polymorph trap, its naturally low AC can prove troublesome unless the player is sufficiently prepared and has poison resistance. Like most demons, it is vulnerable to silver and cold attacks.
Bone devils attack with weapons and with a great hooked tail
which causes a loss of strength to those they sting.