an extremely early creature concept with heavy inspiration from an old minecraft roleplay called The Haunting There are 2 subvariants for these that will be described here.

Normal nightmares

These creatures are created when someone accidently or purposefully destroys their universe and end up in the In-Between Where they are torn apart atom by atom and put back together eventually being put back together incorrectly having new limbs or missing limbs and features.

looks

• Looks of this species varies but follow this general description.
• Dark void like skin.
• bright white or pink eyes most of the time without pupils but still showing a look of fear or panic.
• never looking like the original species, most of the time incomprehensible from the original.
• multiple limbs that the original creature wouldnt have had,
• anywhere from 1 to 10 feet tall.

Example

Meet Billiam

Abilities

• Teleportation for up to 80 meters
• slight reality warping allowing them to create small objects most of the time food.
• night vision, Depending on eye colour their vision will also be a purplish hue.
• can see up to 50 meters before their vision blurrs.

Behavior

This depends on where you encounter the creature

• Skittish unless cornered where they will become very hostile, most of the time not stopping till one of the parties is dead.
• inside the In-Between they are very curious and will normally wander towards anyone there not being torn apart.

Elder Nightmare's

These are nightmares who have lived long enough, normally about 200 years.

looks

• can be anywhere from 20- 40 ft tall, Can also shrink themself down to be 1-10ft tall but this is rarely done.
• Multiple limbs where they shouldnt be. normally with 6-8 eyes somewhere on their body,
• each eye a different colour, ranging from yellow to blue, pink,purple , white.

Abilities

• has the same as the previous evolution
• more reality bending, Can now create objects up to half its size, as well as delete inorganic matter up to 100 pounds.

Behavior

• somewhat friendly, Will try and approach people if it spots them
• will only attack if attacked.
• Curious, Will follow people around as if studying them.

Arch Nightmare

These creatures are Dangerous, and are universe level reality warpers, very few exist.