Ultimate Custom Night

The game allows the player character to choose from 50 characters from the first six main Five Nights at Freddy's games and FNaF World, and set their difficulty levels for the night from a minimum of "0" to a maximum of "20". During the night, the player must keep track of several mechanics, such as doors, ventilation systems, and air duct systems to avoid being attacked by the animatronics.[2] The player can earn "Faz-Coins" to buy power-ups, plushies to stop certain animatronics, and a "Death Coin"[3] to eliminate an animatronic of the player's choice from the current night. The player is also able to select the office setting, pick power-ups that may help them during the night, and select 16 challenges available to them. The objective is to survive from 12 a.m. to 6 a.m., with each hour in-game lasting 45 seconds. In the final release, 59 characters from the franchise were included, with some appearing without the player's choice.[4] Of these extra nine, Dee Dee from FNaF World has the ability to randomly spawn and summon either a character that isn't currently active or one of six that are unavailable to the player.[5] An easter egg involving using the Death Coin on Golden Freddy when he's the only active character on a night and set to "1" difficulty triggers a jumpscare from Fredbear,[6] the earlier incarnation of Golden Freddy who had previously only appeared in minigames.

While Ultimate Custom Night is not as narrative-focused as previous installments in the series, players have still come up with several interprations of the game. The most widely accepted theory is that players assume the role of William Afton, the franchise's main antagonist, who is trapped in a purgatory-like state after the events of Freddy Fazbear's Pizzeria Simulator, and that Afton's repeated deaths at the hands of the animatronics he had helped to create are a form of punishment for his crimes. The one responsible for Afton's torment is implied to be Cassidy, one of his victims whose spirit possesses the Golden Freddy animatronic, who is indirectly referred to as "the one you should not have killed" by some characters during a game over.[7] This theory is supported by an easter egg that is accessible by having Old Man Consequences (from FNaF World) be the only active character on a night and set to "1" difficulty. Upon catching a fish, an 8-bit minigame will be triggered, where players control a bear sprite (possibly Golden Freddy) and can speak with Old Man Consequences, who will tell them to leave the "demon" (implied to be Afton) to his own demons and rest their soul. The only way to end the minigame is to quit the game or drown in a nearby lake, which will cause the game to crash.

In February 2018, after the release of Freddy Fazbear's Pizzeria Simulator, Cawthon announced in a Steam post that he would think about gaining help from larger publishers in making future games. In an edited version of the same post, he added that he would be developing an "ultimate custom night" add-on for Freddy Fazbear's Pizzeria Simulator,[8] which, as revealed on his website, would have more than 50 animatronics from the entire series attacking the player. After realizing the size of the update, Cawthon decided to make it its own separate game. As he was programming the characters in the game, he would update the "progress bar"[9] on his website, along with a brief description of the characters on a Steam post. The game was due for release on June 22, 2018. However, in a Steam post by Cawthon, he revealed that he had planned to release the game on that day, but he had promised YouTuber Lewis Dawkins (known online as "Dawko") that he would not release it before he came back from a cruise vacation, so he would wait until Dawkins returned from vacation on June 27 to release the game.[10]

Ultimate Custom Night received mostly positive reviews. Rock Paper Shotgun deemed the game "an intriguing mess",[7] with PC Gamer calling it "a neat, customisable take on the classic survival horror formula".[1]