Weapon (any sword), rare (requires attunement) · 2024 version below
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.
The 2024 Dungeon Master’s Guide revised the magic items, and the SRD 5.2 carries the new text. What changed:
Same rarity and attunement; the text is reworded for the 2024 rules glossary.
When you attack a creature with this magic weapon and roll a 20 on the d20 for the attack roll, that target takes an extra 15 Necrotic damage if it isn't a Construct or an Undead, and you gain Temporary Hit Points equal to the amount of Necrotic damage taken.
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