Springtrap Kasey is the main antagonist and only true animatronic in Five Nights at Kasey's 3. She is a massively-damaged Pup animatronic/springlock suit, as well as the only antagonist that can kill the player and give them a Game Over, as the phantom animatronics can only jumpscare the player and impair their vision and/or hearing.
Appearance
Springtrap Kasey is an early model of a original Kasey Brown suit, as she is referred to as Spring Ryder or Spring Brownie (but for Spring Ryder ... A pup size). by the Phone Guy on Night 5 and by the boy in the Night 3 minigame of Five Nights at Kasey's 4.
She is a heavily damaged Pup animatronic/springlock suit of an olive drab color with darker colors on his stomach and insides of his ears. A great portion of her right ear is missing with wires sticking out of the stump left behind. Springtrap Kasey's entire body is torn and tattered with gaping holes exposing caging and wires throughout, thus making Springtrap Kasey appear much more macabre-looking than any of the other animatronics from any previous installments in the series. Her brown/green nose has an irregular squarish shape due to deterioration. While both hands and feet are attached and generally intact, her legs are entirely stripped from the mid-shin down, fully exposing endoskeleton metal and wiring. Several finger joints from each hand are missing their suit overlays. The middle and pinky fingers of his right hand are notably missing their fingertips. A single black button can be seen on the middle of his chest. If look closely to the large hole from his chest which is located under his button, there are multiple red lines.
Her endoskeleton feet appear wedge-shaped with each sporting five toes. As of 8/8/16, pictures of an early Springtrap Kasey model show her visible endoskeleton torso in a shape of an upside-down triangle. It has six "ribs" that almost act like real ones. It also has several "blood-veins" drooping on each side.
Both of Springtrap Kasey's eyes are properly set inside his head and appear to be pale gray in color. Oddly enough, the eyes themselves are larger, matching to those from an animatronic than a human, or a Pup as the corpse contained inside Springtrap Kasey is that of an animatronic endoskeleton (with the mummified skull, innards, and blood-veins her only remains). However, the eyes are also deteriorated and printed with nearly visible blood vessels, causing them to look rather eerily Human or Puppy-like. Each iris is black and grayish-green in color with glowing white pupils.
She does not typically open his mouth - instead, Springtrap Kasey wears a permanent, wide grin as the material surrounding her teeth has deteriorated. The exceptions to this are during his second jumpscare, the main menu, on CAM 15, his rare boot images, and Ashley Strickland's "Thank You!" image.
Close examination of Springtrap Kasey and the rare boot images depicting her show that there appear to be human or Pup remains within the suit. When viewing the torso and other exposed sections of the endoskeleton, there are chunks of dark pink material that resemble human or Pup innards. Her neck is covered with lines resembling blood vessels. In the boot images, Springtrap Kasey has her jaw open and is pulling the suit's head up, revealing a mummified-looking human or Pup head. It is reddish-pink in color with its eye-sockets larger than the eyeballs. Its mouth always remained open with crooked teeth and what appears to be few long strings. The jaw and teeth of the head can be briefly seen during his second jumpscare, and can also be seen when he's on CAM 15. The corpse's head can also be seen more clearly from Springtrap Kasey's early model screenshot. It is revealed in the end-of-night minigame (after completing Night 5) that these are the remains of Purple Guy/Pup after he was killed by the springlocks within the suit. Strangely enough, from Springtrap Kasey's render modelling screenshot, Purple Guy/Pup's corpse doesn't have any ears at all, though the ears may have rotted away over the years.
~ W.I.P ~