───────────────────── ACT I – A Rift in Code and Space
The battlefield was in ruins. Debris smoldered beneath a dark, fractured sky. Among the wreckage, a lone Indie Cross drone, armor torn and circuits exposed, hovered erratically. Sparks arced from its core, warning systems blaring in static shrieks. The drone's HUD flickered—a shattered grid of data and red alerts. It had failed its mission.
With protocols collapsing, the drone enacted its final contingency: escape. A swirling red ring of light pulsed from its emitter—its portal drive. But something was wrong. Its internal energy grid was unstable. The calculations scrambled. The circle collapsed inward before flaring outward in a jagged, unnatural spiral. Space buckled.
It didn't teleport.
It disappeared.
Silence.
Then—
The drone reawakened. No warnings now, no HUD, no sound. Only black. A darkness not of absence, but of purpose. The Void.
Movement.
Not sound—but pressure. Awareness.
From the depths stepped W.D. Gaster.
He did not walk. He emerged, as if always there, unnoticed until he chose to be seen. Half-formed, his face glitching like a broken file, eyes fixed not on the drone—but through it. His expression was not malice. Nor curiosity. Something colder: calculation.
The drone trembled, energy still leaking from its red beam emitter, struggling to aim.
But Gaster raised a single finger. Time in the Void bent to his gesture. The beam froze mid-flicker—its red light hanging in the air like caught silk. Gaster stepped closer, inspecting the beam, not the drone.
And then—he smiled.
"You are not from this timeline," he said. "But you bring something... familiar."
With a motion, he touched the beam.
A ripple of red cascaded through his body. Instead of corrupting him—it merged with him. His bones cracked with the sound of static and rewinding tape. Symbols burned across his hands. His eyes glowed crimson. The Void shook.
The drone screamed a digital cry—its last.
Then: nothing.
Only Gaster remained.
Changed.
Elevated.
Nightmare.
─────────────────────── ACT II – Nightmare Contagion
The Void no longer held Gaster—it obeyed him.
Where once he observed in silence, fragmented across timelines, now he stood unified and unbound. The red corruption that had once belonged to the drone pulsed inside him like a second heart. Not mere power—a virus of reality, weaponized by a mind that had always existed just beyond comprehension.
And now… he was watching everything.
From within the depths of the Void, Gaster opened invisible windows—slices in space-time that bled with static and distortion. Through them, he peered into the multiverse. Alternate Universes (AUs), once self-contained, began to flicker, their laws bending under the strain of something foreign invading their code.
His experiment had begun.
UnderVerse trembled first.
Multiversal timelines, once curated by XGaster and entangled in the threads of Ink, Error, and beyond, began to destabilize. Where once paths were linear—fractures formed. Entire AUs began slipping into something... darker.
Gaster didn't attack them.
He infected them.
The red pulse—a silent, creeping energy—flowed into their roots. Timeline after timeline, AU after AU, reshaped under the lens of Nightmare.
In Swapfell, benevolence turned to calculated tyranny. Flowers bloomed with eyes. Snowdin froze time itself.
Horrortale became unrecognizable, its madness sharpened with clarity—every monster grinning with intelligent malice instead of primal fear.
The world of Outertale cracked as stars began screaming, their gravity warped, orbiting a new source: a red-black eclipse blinking from the Void.
Glitchtale – Under Gaster's Nightmare contagion, its glitch‐spawning spells spin out of control: portals slam shut mid‑cast, undead Frisk echo in every reflection, and Sans's teleport splinters into jagged tears in reality.
Even Handplates, a story rooted in suffering, was rewritten—not as tragedy, but as triumph in torment, with the brothers smiling at their own descent.
The Omega Timeline, built to contain anomalies, began glitching. Chrono-anchors broke. Entities designed to stabilize it were infected, corrupted, or twisted into new forms.
All changed—without a single touch.
Nightmare Mode wasn't just power. It was philosophy. A blueprint, embedded and unleashed, rewriting the intent behind every AU's origin.
This was no conquest.
It was research.
Each corrupted AU was a test tube. Gaster observed them all simultaneously, documenting. Calculating. Refining.
And in one corner of the multiverse... in a timeline stained red long before he touched it...
Dusttale stirred.
─────────────────────── ACT III – "Fractures of Power"
──────────────── 🩸 ACT III.I – "Dust Rewritten in Nightmare"
The void trembled. NM!Gaster stood adrift within it, his hands behind his back, gaze fixed outward into the chaotic lattice of timelines unraveling before him. AUs flickered like dying stars—one by one consumed, not by war or mercy, but by something far more elegant: corruption.
His corruption.
Each world affected by Nightmare power twisted uniquely. Some imploded, others bloomed into exquisite disarray. But one, one AU caught Gaster's attention—a familiar one.
Dusttale.
Its soulscape was fractured. Drenched in the desperation of a single monster endlessly resetting, killing, trying to "save" everyone from their fate. It was broken already. No push was necessary… but an upgrade, now that was interesting.
NM!Gaster's hollow grin widened.
"Let's test the resilience of a broken heart…"
Dust wandered through Waterfall. His steps were slow. Heavy. The echo of drips in the dark now nothing but reminders of the friends he'd already killed. His dust-covered sweater clung to his frame, soaked in guilt and false purpose. The weight of genocide pressed on him—but still, he walked.
Then the ground shifted.
Suddenly, violently—reality itself glitched.
The serene murk of Waterfall stuttered into a void-black frame. The air froze in place, as though time itself blinked. Dust gasped, eyes darting as reality warped back into a different version of Waterfall—a hall, stone‑cold and silent.
At the far end stood a grey door, alien to anything that belonged in the Underground.
It pulsed.
Black flames licked through its seams, burning nothing yet scorching the very light around them. Dust hesitated, Soul flickering instinctively in warning—but he stepped forward. Slowly. Drawn like a moth to dread.
His hand reached for the knob—
But before he could touch it, the door creaked open on its own. Slow. Deliberate. The sound was wet, like bones bending backward.
Dust took a cautious step inside.
And then—it hit.
A beam of pure black smoke blasted from the doorway, too fast to react. It slammed into Dust, launching him backward into the far wall with a crack of stone and bone. He coughed violently as darkness surged into his chest, a low hum drilling into his skull.
The grey door began to melt, the frame folding into static, fading from existence as if it had never been there.
All that remained was the black smoke, now coiling tightly around Dust. Thick. Living. It shrieked without sound, writhing like something starved and ancient. In seconds, it grew—forming a massive void sphere nearly double his size, pulsing with red veins and flickers of anti-light.
Inside, something began to change.
The sphere pulsated… once…
Twice…
Then it exploded in silence.
Dust stepped out.
But this wasn't Dust anymore.
His pupils were gone, eyes now streaked with black static and a burning red tear on one side. His sweater had fused into a shifting black cloak of frayed matter, shadowflame licking at its torn edges. His LV radiated like a dying sun. Each breath expelled corrupted dust and bitter regret. His knife—now twisted, jagged, and glowing faint pink—seemed to whisper to him.
He had become NM!Dust—the vessel of a new kind of determination:
"The kind that never stops breaking… until everything's beyond fixing."
───────────────────── ACT III.II – "Errors in Corruption"
Error was enjoying his chocolate in peace, watching a few episodes of UnderNovela, relaxing within the calm hum of static and code. But his expression changed when dark flames—unlike anything he'd ever seen—began seeping through the screens and edges of his space. The show glitched, then blacked out completely.
Error scowled. "What now…"
He stood up, annoyed, casually stepping toward the screens to repair them. But as he got closer, a sudden red beam surged through an unstable portal—silent, fast, and unexpected. The beam struck Error, triggering a violent spike in his glitching. Hundreds of ERROR signs erupted from thin air around him, more aggressive and numerous than ever before.
The red beam destabilized and vanished into raw code, overwritten and absorbed by Error's nature, but the damage was done. He dropped to his knees, clutching at himself as more and more corrupt glitches distorted his form. Something else was embedding itself into his code—slowly, but persistently.
Suddenly, a glowing portal burst open. Ink stepped out, panic already on his face.
Ink: "Error! Something terrible is happening. And as much as I know you'll hate this—we have to work together."
He took a step forward, noticing the corrupted aura now surrounding Error.
Ink: "Error? Are you alright?... You're glitching way more than usual... and... worse than I've ever seen."
Error didn't respond.
His skeleton, normally black and laced with erratic code, was now shifting into something darker—shifting hues between corrupted void-like tones. The colors pulsed like unstable pixels, flickering between shades of darkness no code should have ever held. The glitching had changed—it wasn't Error's glitching anymore. It was something else. Something foreign.
Ink took a step back.
Ink: "...Error?"
Then, another portal opened. Core Frisk appeared just outside it, hesitant.
Core Frisk: "Ink, did you get Error to help?"
Ink didn't take his eyes off Error.
Ink: "Core... get out of here. Now. Something's wrong with him. I think... he's being affected too."
He turned briefly toward Core.
Ink: "Go back to the Omega Timeline. We'll need every bit of help we can get. This is bigger than anything we've ever dealt with."
Core Frisk nodded and disappeared as the portal closed behind them.
Ink faced Error again. The silence was heavier now. Error was standing. Staring directly at Ink. His pupils were crimson red. The glitching wasn't slowing. But neither was it taking full control. Not yet.
The Nightmare energy was crawling through Error's code, slowly converting him—more methodically than it had with others. A different infection. One Error's nature was resisting, but not for long.
NM!Error was becoming inevitable.
And Ink was the only one left to try and stop it.
───────────────────── ACT IV – "The Feast of Collapse"
All was silent in the heart of the Doodle Sphere, yet an undercurrent of Nightmare energy pulsed through every fractured timeline. From the deepest fissures to the outermost strands, NM!Gaster's corruption radiated like a slow‑burn shockwave, touching even the most fortified realms.
🔥 Scene 1: Fatal Glitch
Fatal Error lounged in his private alcove, the hum of stabilized code lulling him into complacency. He was a being of near‑absolute certainty—untouchable by most anomalies. Yet today, the air itself felt wrong. There was a low vibration, like a scream buried under logic.
A tear in the void split open, jagged and bleeding red static.
NM!Gaster emerged from it like a glitch made flesh—grinning, flickering, half-erased and yet terrifyingly aware. Clutched in his hand was a grotesque construct: a malformed drone of warped machinery and bleeding code, humming with restrained power.
Fatal Error's eyes narrowed. His scans bounced off Gaster like they were hitting an anti-pattern. "You… shouldn't exist," he muttered, system parameters scrambling.
Gaster didn't respond.
He just threw the drone.
It spun through the air with eerie silence, crashing to the floor a few feet from Fatal Error—then immediately fired a pulsing red beam upward in a jagged spike of light.
The beam pierced Fatal Error's chest before he could move.
Time fractured. Screens shattered into symbols. The floor rippled into black gridlines. Fatal Error's own form broke into recursive loops, glitching between error states and unreadable fragments of identity.
The drone melted into code.
Fatal Error fell with it—unraveling, not just erased, but absorbed into whatever the drone had delivered. A silent, irreversible overwrite.
When the static settled, nothing remained. No dust. No glitch. No drone.
Only NM!Gaster, floating back into the tear he came from.
His laughter didn't echo.
It distorted.
🌌 Scene 2: The Dinner Table
Far beyond the rupturing multiverse, in a quiet corner of a different void, Zarethra[1] reclined at a polished black table. Her elbows propped on the surface, head in her hands, she watched UltSans with faint amusement as he arranged plates of Karmethis pie and Solmuth pasta with meticulous care.
"Nice work, Azzy," she purred, clapping once. Before he could sit, she winked and merged into his form, causing him to glitch mid‑motion. Shaking it off, he took her place at the seat, and her voice—soft and triumphant—echoed from within him as he tasted the pie.
Above them floated Zeriel[2], arms crossed, a bemused smile tracing his lips. "Well, at least you like my cooking…" he sighed quietly.
Zarethra ignored him, savoring each bite. When she finally rose, she made the dishes vanish in a swirl of shadowed code, then drifted toward the lab doorway.
Zeriel called after her, voice tight with concern. "Remember your classification system? The AU work?"
She glanced back, head tilted. "Yes?"
"It's… unraveling. Something's attacking the timelines. Come see."
Inside the lab, holo‑monitors flickered with red‑tainted maps of the Doodle Sphere and its network of AUs. One by one, they dimmed or fractured into static.
Zarethra floated to the console, eyes scanning the chaos. Zeriel hovered beside her, exhaling a long, weary breath. "I guess we have work to do, huh?"
She shot him a grin as she leaned in close. "Mhm… but you're the one at the keyboard."
He closed his eyes. "Yeah. I've got it. Just… don't take over my body again, okay?"
With a soft laugh echoing in his mind, she melted back into his form. Together—two halves, one will—they turned to face the growing storm of Nightmare corruption spreading through every timeline.
[1] UltChara or UltSans' Chara, with an original name, one for herself, the new her.
[2] UltSans. With a new name as outside the body, he is himself, a new monster soul from Experiment Number Eighteen, and the Next Generation monster.