|“||Forging Material. Found rarely as a drop and by deconstructing rare equipment.||”|
— Item Tooltip
Eye of Q'bthulhu is a forging item that is used in forging and upgrading Shadow rarity items. You can get them by destroying Relic, Resplendent, Shadow, Radiant and Stellar tier weapons, in the Loot Collector and they are the most common item of the Shadow Caches from the Shadow Arenas.
The name 'Q'bthulhu' may be a portmanteau of .qb (Qubicle file) and Cthulhu.