DoomBlade (5e Equipment)
From D&D Wiki
Weapon (Greatsword), Legendary (requires attunement by a non-neutral creature)
A massive Greatsword that's 20 feet long. Once attuned with, it becomes weightless and deals extra 4d12 damage, the damage type of which is based on the attuned creature's alignment. If the attuned creature is lawful good, the damage type is radiant. If the attuned creature is lawful evil, the damage type is psychic. If the attuned creature is chaotic good, the damage type is force. If the creature is chaotic evil, the damage type is necrotic. To pick it up without attunement you must succeed a DC 20 Strength saving throw. Any subsequent action with the sword requires a successful DC 16 Strength saving throw.