Unicorn Meat is the rarest ingredient known, and can be acquired either by trading equally rare Mysterious Machine Parts to Burdley (for Merchants only), or by successfully killing a unicorn during a random event in the forest. A successful kill also nets the hero a rare Unicorn Horn, which is used by the Blacksmith as an ingredient for forging the Doomplate, while an unsuccessful encounter with a unicorn results in a big -40 "Unicorn Horn Wound" buff.
Unicorn Meat can only be used for roasting a large plate of Unicornucopia, which gives a hero a huge +75 "Unicornucopia" buff that lasts for 24 hours. It can also be sold for a large sum, costing 1,000 Simoles when sold from the inventory, and even more when sold through the stall of a skilled Merchant. (But, on patch [2.0.133.00001] it has a glitch where the Merchant tries to sell it on its stall and and receives a message saying: "You have sold your for 0 §")