Sword of Life Stealing [Меч кражи жизни]

Weapon (any sword), rare (requires attunement)

When you attack a creature with this magic weapon and roll a 20 on the attack roll, that target takes an extra 3d6 necrotic damage, provided that the target isn't a construct or an undead. You gain temporary hit points equal to the extra damage dealt.

Source: D&D System Reference Document 5.1, © Wizards of the Coast LLC, licensed under CC BY 4.0.