Nightmare is a fan-made easter egg in Abandoned: Discovery Island.
Nightmare looks similar to Nightmare Photo Negative Mickey from Nightmare Before Disney, but he is yellow and blue, he has more spikes in his body, a hole in his stomach, holes in his head, and 2 eyes that Nightmare Photo Negative Mickey lacks.
Nightmare is not hostile, but will appear in the office at any random time of the night, most commonly at 3AM and onward. Nightmare will stand at the side of your desk, making the lights flicker, and will make a sound of distorted gargling. Nightmare will only appear for 5 seconds, but rarely, he will stay for 15 seconds.