The Sasquatch, Wendigo or Yeti is a monster seen on the whiteboard. No one bets on it.
In appearance the Sasquatch resembles a large, hairy humanoid, akin to the characteristic images in popular culture.
According to a Q&A with Drew Goddard, the item in the basement that would summon it is a jar of Eau de Sasquatch. However, this may have been a joke.
It is unknown who plays the role of the character.
The Sasquatch/Wendigo/Yeti is shown only briefly on a monitor during The Purge in The Facility Locker Rooms beating a member of the Security Force to death. A better view of it can be seen on the special features. He previously appears in an elevator cube waiting calmly on his release
The monster is based on several different creatures. Various Native American legends and reported sightings are the basis of the Sasquatch, also commonly known as Bigfoot. The creature is described as a large, bi-pedal creature with large footprints, an unusually offensive odor, and thick brown or black fur. It is considered a cryptid: an animal whose existence has not been verified and remains largely in doubt. No hard evidence of the Sasquatch exists, as DNA testing of hundreds of supposed samples have all been determined to be from known animals. The creature is the subject of an incredible number of hoaxes, perpetuating belief in popular culture of its actual existence. In western culture, the Sasquatch has become a pop culture icon, often appearing in modern media, such as movies, cartoons, TV shows, commercials, comic books, merchandise and even video games.
The Yeti is a similar cryptid reported to exist in the Himalayan Mountains, originally popularized in the west as The Abominable Snowman. It's appearance is largely similar to the Sasquatch, described as a large, upright walking "man-bear" with black or brown-red fur. Despite this, popular depiction in western media almost universally depicts the Yeti with white hair. Its actual existence is considered more likely than that of the Sasquatch, mostly owing to the isolation of its environment, although it is still largely considered either fictional or a species of bear.
The Wendigo is an amalgamation of a wide variety of creatures from Native American mythology. It is either an evil spirit of the winter, or a human possessed by such a spirit, driven by famine to consume human flesh and/or overwhelmed by greed. The majority of depictions have little in common with either the Sasquatch or Yeti. Most describe it as monstrous and gaunt, with a skeletal or bestial appearance. In some depictions the Wendigo takes on gigantic proportions, growing such that no matter how much it consumes it will always be famished. The legend has many parallels with legends of the Werewolf from Eastern Europe.
Many terror and spoof films use Sasquatch, the Yeti, and less commonly, the Wendigo as a stock monster. The creature and creatures similar to it have been featured in films such as wikipedia:Abominable, Bigfoot, The Legend of Boggy Creek, Ape Canyon, Night of the Demon, Curse of Bigfoot, Night Of The Bloody Apes, Troll Hunter, Wendigo, Night Beasts and several others.