Nightmarens are the main antagonists of the NiGHTS series. They are residents of Nightmare who invade Nightopia  and creations of Wizeman the Wicked. Their purpose is to steal dream energy (ideyas) from humans.
All of the Nightmarens were created by Wizeman with the solely purpose to steal human's ideyas, they can take many different forms and have many different abilities.
The Nightmarens biggest weakness is the ideya of courage, which due to it's enormous power, no nightmaren but the first levels can steal it.
The nightmarens follow a system where they are ranked as first, second or third level nightmarens:
First Level Nightmaren
They where created to be Wizeman's second-in command over the other nightmarens and to steal the red ideya, but for Wizeman's surprise, NiGHTS decided to rebel.
Second Level Nightmaren
Second levels are below power and rank to first levels but above third levels, they dwell in their own Nightmare and draw NiGHTS and the visitor there after NiGHTS had been freed from it's prison, there, a boss battle commences. Each 2nd level and Nightmare is allocated to a Nightopia in order to invade it, lead the third levels and retrieve NiGHTS for Wizeman, second level nightmares have the ability to create their own battlefields.
Third Level Nightmaren
These are all the minor nightmaren creatures that appear throughout the gameplay and come in many forms, from the iconic Shleeps to the small Beezes, their purpose is to invade nightopia and steal ideya. They will attack NiGHTS but are easily dispatched by NiGHTS by Paralooping, Drill Attack, or Touch Dash. They serve as obstacles during gameplay.
They are also known to actually chase and eat Nightopians in Journey of Dreams. 3rd-level Nightmarens are capable of easily beaten if Helen or William toss Blue Chips at them.
The following nightmarens level's are unknown:
It is unclear if Goodles follow the usual level system, their role is to apprehend NiGHTS and maintain and guard NiGHTS captures . They ride huge birds which are unnamed and the bird's level is also unknown.
Unnamed Shapeshifter Nightmarens
During the dreamers intro cutscenes in both games, the first nightmares to be seeing are deformed dark nightmares with red glowing eyes who were disguised as humans before showing their true selfs, in NiGHTS into dreams they appear as deformed monsters, in NiGHTS Journey of dreams, they appear as dark smoke-like creatures with a smiley face.
These nightmares have a very unique behavior, they completely vanish after seeing the light and they are not seeing ever again after the intro cutscenes, it's unknown what happen if these nightmares get the humans or what their purpose is or if they follow the usual level system, however they can manipulate the enviroment just like the second level nightmares, they also appear to be able to either teleport or turn invisible considering they appear out of nowhere in Will's intro, it's also unknown what are the limits of their shapeshifting abilities, considering one of them was capable to shapeshift into a projection of Helen's mom in Helen's intro.
Bomamba's Cat Minions
It's unknown what level Bomamba's cats are or if they even follow the usual level system, however, if they do, they are most likely third level nightmarens due to the fact they can be defeated with a single attack just like the rest of the nightmarens from that level.
During the Cerberus fight, it's possible to spot some crows flying around, however, it's unknown if they are nightmarens, it's even possible that they are just part of the battlefield Cerberus created, if they are nightmarens though, it's unknown if follow the usual level system.
- Unnamed Scrapped Nightmarens: List of nightmarens who were scrapped or disconsidered during the game's development.
- Selph: The most famous deleted character from the NiGHTS series.
- Chamelan and Verol and Gillwing and Pole are the only nightmarens to be based on the same animal (chameleon and tadpole respectively) but to be from different levels.
- Beez Pod is the only nightmaren to not be based on an animal nor to be actually alive.
- In the Archie Comics, it's implied that at least the first and second level nightmarens are antiheroes rather than villains, but they still follow Wizeman's orders because they all fear him, in their single appearance in the fourth issue, none of the second level nightmarens (Jackle, Puffy, Gillwing and Clawz) showed remorse over their creator's demise and they attacked Reala, who self-declared to be the new ruler of Nightmare.
- However, none of them appeared to have any good intention, they all appeared to just care about themselves and power, it's very likely that they would continue destroying Nightopia.
- The nightmaren's ages were never revealed in the games, however, in the Archie Comics, NiGHTS rebelled 100 years before Claris and Elliot were born, confirming NiGHTS age to be at least 100 years old.
- Queen Bella, Goodles and Bomamba's cat minions are the only nightmarens who can't fly.