The difference between a dream and a nightmare could be quite fuzzy. The latter was a subset of the former, after all. There was no natural 'nightmare matter' in Dreamspace, although there was matter that caused nightmares in real life - usually either something with seriously negative psychokinetic radiation, or regular matter with individual psychosomatic effects. No, the only thing determining if a dream was a nightmare was one's subconscious reaction to it. In fact, the very same dream sequence could be a nightmare or a regular dream at different points of the same individual's life, sometimes even merely at different nights.
Normally, 'nightmare' was just a state of sleep in which the sleeper experienced distress. If their mind entered the state of lucidity, or simply switched gears to another scenario, they could move away from the sequence.
However, introducing lucidity into the mix changed the entire equation.
A lucid dream could be described as a dream in which the dreamer's mind was self-aware, and often capable of not just making conscious decisions about how they act, but even changing their inner Dreamscape according to their desires and intentions.
The same could not be said about a phenomenon called 'lucid nightmare'.
While experiencing a lucid nightmare, the dreamer reached the state of awareness of their self, and of the fact they were sleeping. However, this awareness did not directly translate into control. The dreamer did not possess an ability to introduce changes into their inner Dreamscape, nor were they able to make conscious decisions, despite a distinct presence of consciousness. It was akin to only mostly reaching the state of lucid dreaming, but lacking an essential part of it.
In simpler terms, if you were in a lucid nightmare, you would've been aware of the fact you were sleeping, but could only experience the nightmare sequence as it played out. No way to change it. No way to act. Just you being aware of your own helplessness in your own Dreamscape body, as your nightmare followed its script.
She instantly understood this to be a lucid dream - the inner Dreamscape did not try to meld her mind into the dream's point of view, meaning the sleeper was well aware of themselves, easily separating other psyches from their own. But that's where their blessings kinda ended.
The thick, oozing terror pounded through the space at a rate of a frantic heartbeat, slowing one's movements, and clouding the vision. Everything was dark red - like the entire world was drenched in half-rotten viscera. The walls, and the floor, and the ceiling were covered in huge gashes, left by some beast's horrible claws.
And bodies.
Everywhere, were bodies, torn asunder, sliced apart, crushed into paste, eviscerated and half eaten, few remaining glassy eyes frozen in terror and agony. Bodies everywhere, as whatever left them carved a wide swathe of death through this place.
She quickly glanced around. Right next to her, was Honnoji. The poor girl looked as if she would've rather been anywhere else, including her own nightmare, rather than here. A bit further, was Anegawa, busying himself with tearing into one of the carcasses, as if no one's business. And a few meters away, stood Hiei.
She looked as if she had been struck.
And then.
SHRIEK.
A horrible, ear piercing SHRIEK, primal, unnatural and borderline otherworldly, originating from somewhere further into this horrible place. The space around them changed into some other corridor, and began moving around them without any regard for what the group was doing.
The Mimikyu, previously unbothered by what was happening, suddenly jolted backwards, looking around frantically. She could've sworn he was shivering. The Absol next to her cowered, paws covering her ears, eyes full of terror.
"No…" Hiei said silently, then darting away to the centre of the inner Dreamspace, "Inabayama!"
This was either the right or the wrong thing to do, since the moment she shouted, an invisible force took a hold of all of them, determinedly pulling in that same direction, as architecture twisted and shifted to accommodate their trajectory, before depositing them in a wide room that moved around the group as well as the occupant of this inner Dreamspace.
"Inabayama!" Hiei flew closer to the dragon, who was actively running away from something.
"Oh! Hey, Hiei!" the dragon greeted without stopping. She somehow managed to look almost cordial despite the waves of panic emanating from her, "That's weird, are you-"
SHRIEK
"Owww… Damn, that's loud," Goodra winced, "Are you real? Or is this a new nightmare twist?" her eyes shifted to the rest of the group, "Huh, probably real"
"We are under attack," despite her reservations about interrupting Hiei and Inabayama, she explained, "Nightmare-inducing Pokemon"
"And of course, they could not use actual original material," the dragon somehow rolled all twelve of her eyes. Huh, twelve? "Also, I can't stop. Been on a loop for, like, a dozen times already"
The surrounding shadows stirred
"You've been through this a dozen times?!" the Gardevoir looked back to where the Goodra was running away from, murder clear in her eyes.
"Yeah. Chase, reach the end, reset. Look, I might not know what's happening-"
"Lucid nightmare," she explained both to Hiei and Inabayama, "No control, just awareness."
"…I might sorta know what's happening, but I have no idea what to do. Any ideas?
"Transition into full lucid dreaming. Either that, or solve the nightmare sequence"
"Cool," Goodra sighed, "Any ideas how to-"
SHRIEK
This one was close. Way too close.
"No time for a lesson," Hiei noted, floating to a space behind the dragon, as some sort of a horrible dark figure jumped out of the shadows and gave them chase, skittering along ground, a wall, then ground again.
Then, it POUNCED.
Hiei met the shadow head on, claw meeting claw, air rippling from the sudden clash. Both were thrown back, Gardevoir stopping mid air, while the monster skidded several meters across the floor, screeching to a halt on all fours, and advanced again. This time, the shadow sprang to the left, then to the ceiling, then straight at Hiei, aiming several vicious slashes at her neck and heart crystal - green claws striking in time to block those strikes. If only barely. And with each passing moment, the Gardevoir was getting slower.
This… Was the same issue as with Anegawa's nightmare. The Mimikyu thought himself powerless against Hiei - so in his nightmare, she was practically invincible to him. Inabayama thought herself incapable to escape from this shadow - and so, it was making everyone around it slower and slower.
And Inabayama could not even help, still stuck trying to run away, also getting slower and slower with each useless step.
"Honnoji!" the Gardevoir yelled, even as the shadow's claw tore into her arm, drawing blood, "Nail at eleven."
Next moment, multiple things happened almost simultaneously. First, Gardevoir made half a step back, grabbing the shadow's extended arm with her healthy one. Second, the monster was thrown to the side, and already began course correcting mid air. Third, something impacted with the thrown shadow, piercing through its chest and the space behind it, right through the nightmare shell, and into the outer Dreamspace, creating a large enough hole for a ticker tape parade to pass through. Fourth, the shadow fell to the ground, deep darkness dissipating faster than it was disintegrating.
From the ground, in a mix of surprise and accusation even as she was slowly disappearing, at Inabayama stared another Hiei.