Although it isn't technically a monster, it works like one, so, it makes more sense to belong to the "Monsters" category. This skull is capable of flying (hovering) and patrols the dungeon. It can be encountered in Nights 6 and 7.
The Flying Skull can be heard from a distance, laughing. Its red light illuminates the walls, making it possible for the player to tell it’s in the other side of a corner and also see it from a long distance. It seems to spawn at a random location. It doesn’t know the player’s location and moves randomly within the dungeon. Its spawns and disappears in different random locations. It moves much faster than Mary and faster than the player walking. When it finds the player, it chases them and lands a hit on them, which results in it disappearing. It will respawn later in another location. Although it is not dangerous alone, it can be if other enemies happen to be around. If the player has already received damage before encountering the Flying Skull and hasn't healed yet, it could kill them.