The Stag is an unnamed entity that makes various appearances throughout Season 1, 2, and 3 of NBC's Hannibal. Due to its lack of canon title, the Stag has been given numerous monikers such as The Nightmare Stag, The Shrike Stag, and The Raven Stag. For the simplicity of the wikia page, it will be dubbed as the Stag.
The Stag appears to Will Graham as a fully grown bull American elk, with between 6-8 tines on its antlers. To coincide with the symbolism of the Minnesota Shrike as well as the crows pecking at the corpse impaled on a stag's head, the Stag is adorned with broad plumage, which covers the majority of its body.
While it is only a hallucination, it bears similar qualities to a mythological Wendigo, which is said in Algonquian culture to be a half-man-half-beast monster associated with psychosis and cannibalism. The comparison is especially strong later on in the series when the Stag takes the very shape of Hannibal Lecter as the Wendigo in Will's hallucinations.
A nearly identical sculpture of a stag is located in Hannibal's office, and Will first begins to see the apparition after he begins sessions with Lecter. Hannibal later uses the sculpture as a weapon to murder Tobias Budge by bludgeoning him to death.