"Unveiling Diablo 4's Rarest Items and Gems Guide"

Adam Jackson, lead class designer of Diablo 4, has clarified that the six rarest unique items in the game can drop from level 85+ enemies and anywhere a regular unique item can drop. The items are Andariel’s Visage, Doombringer, Harlequin Crest, Melted Heart of Selig, Ring of Starless Skies, and The Grandfather, and always drop at 820 item power. Jackson also confirmed that there are currently only six of these items in the game and they are "realllly rare".