Bloodthirster Scimitar

This carefully carved bone scimitar belonged to a cult of vicious monks whose extraordinary bloodlust and strength have been all but entirely erased from history. While you hold this magic sword, you have resistance to necrotic damage. When you take the Attack action while holding this sword, you can choose to forgo one of your attacks to sacrifice your own blood. When you do, you take 1d6 + 3 piercing damage from the sacrifice. This damage ignores resistance and immunity. This self-inflicted harm empowers the sword, granting you a cumulative +1 bonus to attack and damage rolls made with this magic weapon that lasts for 1 minute, up to a maximum bonus of +3. While the sword is empowered in this way, it deals an extra 1d6 necrotic damage to any target it hits.

Proficiency: martial, scimitar Source: The Griffon's Saddlebag: Book Two p. 48 (Third Party)