Bloodrot

wondrous item (blood), rare, requires attunement   To attune with this item, you need to inject it in your blood, if you do not possess blood, you cannot attune to it. This rotten blood then merges with yours and increase the power of your fists. You gain a +1 bonus to attack and damage rolls made with your unarmed strikes. In addition once per turn on your turn, you can coat your fist with negative energy (no action required). When you do so, your next successful hit this turn deals an additional 1d6 necrotic damage. Alternatively, you can deal 1d4 necrotic damage to yourself (which cannot be reduced in any way) to increase that damage to 1d10. On a hit, you choose one additional effect between the two following:  

Mark of Death: The target’s hit point maximum is reduced by an amount equal to the necrotic damage dealt. If this effect reduces a creature’s hit point maximum to 0, the creature dies. This reduction to a creature’s hit point maximum lasts until the creature finishes a long rest or until it is affected by a spell like greater restoration.

False Mark of Life: You gain a number of temporary hit points equal to half the necrotic damage dealt. Plants and Undeads are immune to this effect. Curse of Killing: While attuned to these fists you cannot choose to knock a creature unconscious when you bring it to 0 hit points, you instead always deal lethal damage. This curse is hidden from any kind of magic made to detect it, until it activates for the first time.