Actions

Multiattack. The devil makes three attacks: two with its claws and one with its sting.   Claw. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 8 (1d8 + 4) slashing damage.   Sting. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) piercing damage plus 17 (5d6) poison damage, and the target must succeed on a DC 14 Constitution saving throw or become poisoned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.   Variant: Bone Devil Polearm
Some bone devils have the following action options.
Multiattack. The devil makes two attacks: one with its hooked polearm and one with its sting.
Hooked Polearm. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 17 (2d12 + 4) piercing damage. If the target is a Huge or smaller creature, it is grappled (escape DC 14). Until this grapple ends, the devil can't use its polearm on another target