The Fallen are a group of enemies that make their first appearances in the Basement.
They appear to be dismantled, misused, and rusted endoskeletons that were intended and implied to be the endoskeletons of Freddy, Bonnie, Chica, and Foxy. They consist of Endos B, R, C, and F, or "Angel", "Blue", "Mouth", and "Red" respectively. They are, as told by the game's creators, doppelgangers who didn't make it to the real world, but are still in their own paranormal world. Considering that, it's unknown how they're able to harm Scott in the attic.