Foxy (Anime)

Foxy (also fully known as Foxy the Pirate) is an animatronic pirate fox as well as the main male protagonist/Antagonist of the anime. He was originally a human but he got killed by purple guy, he could have avoided this if he followed Uni's (Unknown's) directions and stayed far away from him. His mind is still foggy from the event and he only knew that Unknown tried to save him, but failed. He also has the ability to turn into a human, much that he enjoys doing when he's around Unknown. Ever since the events he has held a special place in his heart for Unknown, which means he has developed feelings for her unknowingly. Due to the events that happened in 1987, "the bite of 87", he has been locked inside pirates cove and he is "Out of order", which caused Unknown to be worried for him, which he finds 'too cute for him to handle'.

The Children
Scott Cawthon's hinting of paranormal activity within the pizzeria gave rise to speculation that the ghosts of the five children (and the other victims) might have possessed the animatronics, which caused their macabre and violent behavior.

Another theory speculates that the missing children were stuffed into the five animatronics. This would explain the animatronics' foul odor, the leaking blood and mucus, and the parents' comparisons to reanimated corpses. No one knows what happened to the sixth child though it is believed that the sicth child may have been stuffed into Golden Freddy. This could explain why Golden Freddy has a little girl's laugh. However, it is possible that all of the children were killed and disposed of in a more traditional way.

The Killer
The anime doesn't confirm whether the person convicted for the incident was actually the murderer or if the children were stuffed into the animatronics.

Others believe that it was a homicidal employee (as they would have access to the costumes and the animatronics' AI controls), though the newspaper says nothing as to whether the killer was an employee.

It is strongly hinted that the killer was the Purple Guy from the Death Minigames. Upon the completion of the fifth night of Five Nights at Freddy's 3, the player plays as the soul of a dead child, confronting Purple Guy in a room with the four other dead children watching. Purple Guy attempts to hide inside Springtrap, but once in the suit, he misuses it. This causes the locks that held back the animatronic parts to break, causing the springs and other various parts inside the suit to pierce into Purple Guy's body and cause him to die. This also adds to the theory that the man who was supposedly convicted for the murders (as found in the newspaper clippings from the first game) was not actually the killer, as Purple Guy is supposedly free during the events of the minigame.

Night Guard
A variation of two certain theories speculates that the murderer may have been a previous night guard, which would explain why the animatronics are so determined to reach Mike Schmidt (and supposedly Phone Guybefore him, as heard during Night 4's phone call). Since the killings may have occurred after-hours, this theory raises the possibility that the victim's souls haunting the animatronics want revenge but can only remember for certain that they think the killer might have been the night guard.

Phone Guy
Another hypothesis proposed by fans is that Phone Guy is one of the likely candidates of the Missing Children Incident. Purple Guy appears to be wearing a security badge in the "SAVETHEM" death minigame while Phone Guy was the night security guard before Mike Schmidt. Phone Guy also mentions that Foxy was his favorite, giving fans a reason to believe that he was responsible, as seen in Foxy's Death Minigame, the Purple Guy is seen outside Pirate Cove.

However, the third game's Night 5 cutscene indicates that this hypothesis is highly unlikely:
 * Phone Guy knew that getting into Springtrap would result in serious injury or death, but Purple Guy clearly did not give thought to any potential dangers of getting into Springtrap, and put it on, thinking he would be safe. However, just like Phone Guy explained during Night 3's phone call, the spring locks holding the compressed animatronic parts came loose, and the mechanical parts crushed Purple Guy, killing him.
 * Purple Guy also deliberately did what Phone Guy told employees not to do while in the suits: making sudden movements (suddenly standing up quickly) and breathing on the springs (laughing while inside the suit) providing further evidence that Phone Guy was not Purple Guy, as Phone Guy would have known not to perform these actions.


 * Purple Guy dismantles all the animatronics before his death and is killed by being crushed inside Springtrap while Phone Guy is implied to be killed by the animatronics themselves, before they were dismantled.

Other

 * By Golden Freddy's appearance in the second game (with wires popping out of the eyes and shoulders), it would surely be impossible to get in the suit, although, these wires could just be hanging out of the outside of the suit, being barely inside. This could, however, also mean that the wires and beams were removed and the ones seen are just leftovers.
 * Springtrap, however, is another possible candidate given that he is yellowish in color.
 * Given that Golden Freddy has a similar appearance to Springtrap as well as appearing in the mini games alongside Springtrap while performing for children, many believe that Golden Freddy was a suit that could be worn like Springtrap. If this is the case, it is still very possible for Golden Freddy to be the suit used in the murders.


 * There is another recently popular theory that suggests that The Puppet was responsible for the animatronics being possessed. The Death Minigames in the second game seem to back up the idea, as in the "Give Gifts, Give Life" minigame, The Puppet is shown putting the heads of the original animatronics (Freddy Fazbear, Bonnie, Chica, Foxy and Unknown) onto the corpses of children. A sixth child briefly appears before Golden Freddy pops out at the player. In the Happiest Day minigame in the third game, the six children appear wearing their character masks and are joined by the player-controlled child, who is revealed to be wearing The Puppet's mask, indicating that The Puppet is another child's spirit.

The Bite of '87
The Bite of '87 was an incident that occurred in 1987 at Freddy Fazbear's Pizza; it was briefly mentioned by the Phone Guy in the first game. The details of this attack (and the identity of the animatronic responsible) were not given, but it allegedly caused the loss of the frontal lobe of the victim's brain.

The incident contributed to a loss in the restaurant's reputation, which resulted in a major drop in business.

As a result of the incident, the animatronics were no longer allowed to wander around the building during the day; the management decided to limit their free-roaming mode to nighttime, so as to "prevent their servos from locking up," as stated by Phone Guy.