The first hints of Nightmare may appear after completing the fifth night, in the "Extras" menu: on the last page with animatronics, there will simply be a question mark. After successfully completing the seventh night, the question mark will change to an image of Nightmare. This is a black translucent animatronic, the exact copy of Nightmare Fredbear in shape. He wears a yellow hat with a black ribbon and a yellow bow tie on his stomach.

History

Almost nothing is known about Nightmare's history. He appears as the final threat in the dreams of the fourth part's protagonist, who successfully defends himself from the monster for two nights. Some time later, the Vengeful Spirit uses Nightmare's image to torment his killer in an endless cycle of comatose visions.

In the FNaF 4 files, the animatronic is referred to as "Shadow" or "Shadow Freddy"[1]. This indicates that Nightmare may actually be a distorted form of Shadow Freddy that has infiltrated the protagonist's dreams. The exact motivation for such actions is unknown, but the short story "Hide and Seek" reveals that shadow entities can feed on fears and other strong emotions of people to grow and become stronger.
In games

Five Nights at Freddy's 4

Nightmare is the game's secret antagonist. The only hint of the as-yet-unrevealed threat's existence appears in the Extras menu after completing Night 5: instead of an image of any character, Plushtrap's render is followed by a mysterious purple question mark. When the player completes the optional sixth night and enters Nightmare Mode, which is the seventh night, Nightmare will appear at exactly four o'clock in the morning, completely replacing Nightmare Fredbear, who had been wandering around the house in previous levels.

See also Nightmare Fredbear

After completing Night 7, Nightmare's image appears in the Extras menu, and the player is given the option to play the hard mode "20/20/20/20", where they will once again encounter the creepy black bear at four o'clock in the morning.

Nightmare's mechanics are almost identical to Nightmare Fredbear's. When he appears, all other antagonists disappear from their positions in the house, and the player will be faced with a single threat for the rest of the night. However, this does not make the game any easier: due to its speed and ability to appear in different places, Nightmare is much more dangerous than all the standard Nightmare animatronics combined.

Nightmare starts his movement from the center of the living room, a special room in the far part of the house, where the player cannot enter, but from where many creepy monsters make their way to him along the corridors. From the central position, he can run to the left or right side of the living room. Already at these positions, he has a choice: he can either go to the opposite side of the room, or enter the corridor from his side (but only if the player does not shine a flashlight there). One way or another, having left the center of the living room, Nightmare does not return there on his own. If he made his way to the corridor, he no longer moves and instead prepares to attack. The animatronic can move from one position to another once every 2 seconds, and this does not depend on random numbers. You can track Nightmare's movements by the loud sounds of his steps, which help you understand which side of the living room he managed to run to. But he enters the corridors silently, so it is quite easy to understand at what point he approaches the bedroom: if after a series of steps there is a long silence, it means that the nightmare bear is preparing to attack from the corridor.

When the Nightmare enters one of the corridors, the player is given only 10 seconds on the seventh night and 8 seconds on the eighth to find him. If the Nightmare is not driven away during this time, he will attack. Instead of the usual screamer, the player will see a static image with the animatronic's head, and then the game will restart. To avoid this, you need to close the door of the corridor in which the Nightmare is standing and wait for him to leave. It is important not to make a mistake, since every second counts. The player can check whether he has chosen the right side by shining a flashlight into the corridor. The beam of light should reveal a monstrous figure right at the door. However, you should not rely on the light, because this time it is more harmful than helpful: just one second is enough for the Nightmare to attack, reacting to the flashlight. Instead, you should listen carefully and accurately navigate the sound cues. After closing the door, the antagonist goes to the opposite side of the living room, stomping loudly. Then he can immediately go into another corridor, so you should not hesitate during the night.
Nightmare can move not only through the living room and corridors, but also immediately move to the closet or to the bed in the bedroom from most positions. He can do this in two different ways:

On the seventh night, if Nightmare has already stood in the corridor for 10 seconds, and the player at the same time runs up to the opposite door, then instead of attacking, the animatronic will move to the closet or to the bed;

Once every 20 seconds, with a 50% chance, he moves to the closet or to the bed, laughing loudly. Such movements are limited: on the seventh and eighth nights, there can be no more than two.

On the bed or in the closet, Nightmare waits 11 seconds, and if the player has done nothing during this time, he attacks. If the player mindlessly runs around the positions in the room, then the attack occurs one second earlier. To avoid defeat, you need to find the place where the bear is hiding as soon as possible. If he is hiding in the closet, then you need to close the doors and wait for him to leave. The disappearance of the antagonist from the closet will be indicated by loud footsteps, and he will appear in the living room. The flashlight in this case does not affect anything, but with its help you can check whether the Nightmare is really sitting among the children's clothes: if so, then the flashlight beam will illuminate an incredibly large head, which will make a strange squeak. If the monster is hiding on the bed, then you need to shine a flashlight on him for two seconds in a row. Then he will go to the living room and again try to get into the room through the corridors. As in the case with the closet, only an impressive head of animatronic squeaks is visible on the bed.

Although sometimes you can understand about the movement of the antagonist into the room by his booming laughter, you should not rely on this sound clue. If the Nightmare is not on the bed, with a 10% chance he can laugh just like that to try to confuse the unprepared player. If he moved instead of attacking, then the player simply will not hear anything.

Initially, the antagonist is active only on two nights: the seventh and eighth. His AI always remains equal to 20. This means that he will move around the positions with a 100% chance.

The player can add him to any night by enabling the "Nightmare All Over" challenge. In this case, Nightmare replaces all antagonists and becomes a threat right from midnight. Like Nightmare Fredbear, the antagonist will confuse the player for the first 20 seconds by constantly making footstep sounds without moving from his place. Most of his mechanics do not change, but until the fifth night he loses the ability to move to the closet and to the bed, and on the fifth night he can make up to 4 moves.

In addition to the main mechanics, Nightmare has another feature: if the player does not move around the positions in the room for 25 seconds in a row, the animatronic will immediately attack him. However, this rarely works, because Nightmare is almost always on the move, thereby motivating the player to constantly look for him in different places in the house.