Dev discloses Diablo 4's rarest unique items, what they are, and how to get them

pcgamer.com:

Diablo 4's class designer Adam Jackson has dropped details on the rarest Unique items to be found in Diablo 4, from that one cool hat to a sword which is the sire of all those other swords. It's a sudden end to lots of guessing about which items were in, how many, and where they could be found.

Hello! I wanted to clear up some details on the rarest Unique items in Diablo 4.1. They can drop from level 85+ enemies2. You get them anywhere you can get a regular Unique, and they always drop at 820 ipower3. We currently have 6 of them in the game4. They're realllly rare! pic.twitter.com/pVVj5DTEaUJune 24, 2023

The six rarest uniques are sword Doombringer, two-handed sword The Grandfather, the Ring of Starless Skies, helmet Andariel's Visage, the helmet Harlequin Crest, and the amulet Melted Heart of Selig. For my money, «Melted Heart of Selig» is the one with the most kickass name but it is a close contest.

Those six extra-super-rare Uniques can drop from level 85+ enemies, and can come from anywhere you get a regular Unique. They always drop at item power 820, says Jackson, and «They're realllly rare!» Sounds to me like it's time to bust out that list of where certain item types can be found most often.

Diablo 4 dedicants have been frantically trying to figure out how to retrieve the game's rarest loot, disentangling their individual experiences from the collective to collate reams of information to one unified end: How find demon to kill demon to get item. It's the same spirit that has had them untangling spreadsheet-confounding reams of information about world bosses. Or has others searching high and low for secret cow gods.

Jackson later followed up to explain a little more about how to get these six rarest uniques.