Appearance and Characteristics
The Giant Cat is a normal looking house cat, but of enormous size. Based on its appearance; white fur with slick black and grey features, it could possibly be a Siamese Cat.
Since the Giant Cat is locked inside the Facility, its possible it is harmful to humans in some way or another. Its preferred way of killing its victims could be scratching, eating and biting them, as cats do with birds and small rodents.
The item that summons the Giant Cat is unknown, but it could be a number of things; a cat toy, cat collar, or a sack of catnip.
The Giant Cat does not make an appearance during the Purge. The only time it is seen is during an early version of the elevator cube scene of the film where it is seen standing idly in its Cub Prison.
It is difficult to say what inspired its creation, though it may be just a joke or filler monster. Possibly based on the trope of many horror movies, TV shows and other media where animals in gigantic sizes destroy cities and kill people or when a character shrinks down and usually have normal sized house cats as obstacles for the characters.
One source of inspiration may be The Incredible Shrinking Man (1957), when protagonist Scott Carey, at his doll-sized stage, must defend himself from his own pet cat. Another influence could from the 1967 StarTrek episode Catspaw, where Capt. Kirk and Spock are menaced by a being transformed into a gigantic black cat.