Hateful Hook

Weapon (dagger), very rare (requires attunement)

This jagged hook straps onto your forearm and functions as a +1 weapon. Hit points lost to the hateful hook’s damage can be regained only through a short or long rest, rather than by regeneration, magic, or any other means.

Once per turn, when you hit a creature with an attack using the hateful hook, you can wound the target. At the start of each of the wounded creature’s turns, it takes 1d4 necrotic damage for each time you’ve wounded it, and it can then make a DC 15 Constitution saving throw, ending the effect of all such wounds on itself on a success. Alternatively, the wounded creature, or a creature within 5 feet of it, can use an action to make a DC 15 Wisdom (Medicine) check, ending the effect of such wounds on it on a success.

Finally, a hateful hook is imbued with a spirit of bitter vengeance. When you roll a 20 on your attack roll, the target takes an extra 1d12 piercing damage against any creature that has attacked the wielder since the end of his last turn. This ability also applies against any creature that has designated the wielder as its prey in some way (GM’s discretion, by way of example, via Hunter’s Mark or an oathbow’s sworn enemy ability). If a creature using such an ability has damaged the wielder since the end of its last turn, the hateful hook automatically deals an additional 1d12 necrotic damage on a successful hit.

A hateful hook works best if the wielder has lost a hand; if strapped on over an existing hand, the wielder has disadvantage on attack rolls made with it.