In some early concept arts, it was revealed some never seen before Nightmarens. These Nightmarens were either scrapped or disconsidered during the game's development for unknown reasons.
Unnamed Pterodactyl-like Nightmaren
In early concept arts it's possible to find a Pterodactyl-like Nightmaren. It has most of its body inside the egg and its head, wings and tail being outside. It's unknown if this Nightmaren would be a boss or an enemy.
Unnamed Round Bird-like Nightmaren
A round bird-like Nightmaren can be found in early concept arts for NiGHTS into Dreams. It appears to be a round blue crow. Its wings are bizzarely round as well and it has tiny hands which are barely visible. It's unknown if this Nightmaren would be a boss or an enemy.
Unnamed Star-like Nightmaren
An unnamed star-like nightmaren can be found in early concept arts for NiGHTS into Dreams. It appears to be a small twinkling star with big eyes and red feets. It most likely was a third level Nightmaren due to its small size and simplistic design.
Unnamed Squid-like Nightmaren
A squid-like Nightmaren can be found in early concept arts. Jugding by his colors, face and the fact that he is next to an early version of Puffy, the squid character is most likely a very early version of Gillwing. Though, the Nightmaren could still have a different name and boss battle strategy.
Unnamed Cat-like Nightmarens
An Early concept art reveals two scrapped cat Nightmarens for NiGHTS into Dreams who are early versions of Clawz. One of them is a round red cat with pink spots, yellow stripes and a sinister smile. This cat bears a strong resemblance to the Cheshire Cat from Alice in Wonderland. The other is a white female humanoid cat with red stripes.
"More NiGHTS" Icon Nightmaren
In the NiGHTS into Dreams official japanese website, there is an icon with a never seen before character's head and the message "More NiGHTS" displayed under it. The character looks similar to NiGHTS and Reala, but has different colors. Their head and hat shape are also unique in that they curve to the sides rather than the back. Despite the unique design, it is possible that the character is just NiGHTS, as the head appears in some of the game's ads.
Interestly, by inspecting the game's files, it is possible to find scrapped head items which greatly resemble the More NiGHTS icon character.
Frozen Bell's Snowman character
In the level Frozen Bell, as well as in the Christmas NiGHTS version of Spring Valley, the Nightopians may build a snowman version of an unknown never before seen character who may be a scrapped character. It is currently unknown if this character is a Nightmaren or not.
Unnamed Nightmaren from Puffy's mansion
See main article: Crewle
However, there is one painting of an unknown never-before-seen Nightmaren among them, which is only visible if the player holds and spins Puffy in a very specific location of the hallway after the kitchen.
This Nightmaren somewhat resembles a blue tadpole with green spots and a yellow head. It is currently unknown where this Nightmaren would be featured and why it was cut.