Bone Whip

Weapon (whip), very rare (requires attunement)

This whip is constructed of humanoid vertebrae with their edges magically sharpened and pointed. The bones are joined together into a coiled line by strands of steel wire. The handle is half a femur wrapped in soft leather of tanned humanoid skin. You gain a +1 bonus to attack and damage rolls with this weapon. You can use an action to cause fiendish energy to coat the whip. For 1 minute, you gain 5 temporary hit points the first time you hit a creature on each turn. In addition, when you deal damage to a creature with this weapon, the creature must succeed on a DC 17 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage dealt. This reduction lasts until the creature finishes a long rest. Once used, this property of the whip can’t be used again until the next dawn.