Unicorn

The Unicorn is an animal Monster kept in the Facility. It is listed on the Whiteboard and is bet on by the Engineering department. It is seen once during the System Purge.

Physical Description and Attributes
The Unicorn resembles what a typical unicorn is from fairytales and mythology. Here, it is a large all-white horse with one long and sharp horn on the top of its head. How the Facility managed to capture such a creature is unknown, but, like all other mythological and legendary monsters/beings in the Facility, its likely the Unicorn is being studied or is in fact hostile and is used to complete sacrifices.

Other than what we know, the Unicorn's behavior and life are a mystery.

In the Cabin's Cellar, unicorn tapestry is what summons the Unicorn.

Inspiration
Unicorns have appeared in horror films before, however, it's possible Drew Goddard and Joss Whedon put it in as an inside joke and/or an extremely sarcastic note on how many other mythical creatures and fairy tales have been used in horror filmmaking as evil ones examples being Rumpelstiltskin, Leprechaun; the video games American McGee's Alice and its sequel Alice: Madness Returns; Hansel & Gretel: Witch Hunters and Gingerdead Man. It is also thought to be a reference to Supernatural's use of a unicorn in the episode Plucky Pennywhistle's Magical Menagerie (#7.14), however the release date is only a few months later than this episode. Some people have argued that it may be a metafictional note on the fakeness of the scenario, linking it to the famous origami unicorn in Blade Runner.

Unicorns, despite their majestic and approachable nature in today's fiction, are actually known in lore as being deceptively violent in nature. Traditionally, a unicorn would be drawn to the purity of a virgin, but if one was merely pretending to be a virgin, a unicorn would actually kill that person.

It may also have been inspired by this:
 * Celtic mythology
 * Late antiquity
 * Heraldry
 * German folklore
 * Scandinavian folklore
 * The Marvellous Land of Snergs
 * The Chronicles of Narnia: The Lion, the Witch and the Wardrobe
 * The Chronicles of Narnia: The Last Battle whose cover is pictured below

Additionally, unicorns have appeared a few occasion into dark fantasy movies like Black Moon (1975) and Legend (1985).