Hemorrhage (5e Feat)
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Prerequisites: Proficiency with a weapon that deal slashing or piercing damage
You can make your opponents bleed with deep wounds. You can use an action to make a special attack with a weapon that deals slashing or piercing damage. On a hit, you deal damage as normal and the creature must succeed on a Constitution saving throw with a DC equal 8 + your proficiency bonus + your Dexterity modifier. On a failed save, on the start of each of its turns, the creature will lose a number of hit points equal to the damage die of the weapon.
Each time a creature fails the saving throw of this attack, the damage dealt by the wound increases by a number equal to the damage die of the weapon.
This feature doesn't work against constructs, plants, undead and creatures without blood (at the DM's discretion).