Gaster Blaster Transformation Oneshots (ON HIATUS)

No One Will Ever Know...

   Alright, so as many of you probably know, Toby Fox recently released chapter 1 of a new game involving some of the beloved Undertale characters we've come to love so much.
   However, this new game is by no means, connected to the canon Undertale universe. Toby Fox confirmed himself that it takes place in an alternate universe/timeline.
   If you haven't figured it out yet, this oneshot is gonna be DeltaRune themed.
   The reason I wanted to write this is because of Sans's role in the game. From what I understand, Sans is a shopkeeper and he's just moved in town with Papy. He knows nobody, save for a couple of major characters from the old game (for example, Toriel and Alphys). But even the ones he does know, he doesn't really know much about them.
   I wanted to play with this idea a little bit.

   Anyway! Without further adieu, let's get on with the oneshot!
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   Sans was standing outside his shop, staring out across the street vacantly. God, it was so weird being here now.
   Moving had been a lot more stressful than he'd expected. And it wasn't just unpacking boxes and trying to get his shop up and running. Being in a completely unfamiliar place, with a hundred total strangers all around you...
   He didn't really like it too much. He could tolerate it, sure, but he sure as hell didn't like it.
   He missed being in the small town he'd lived in before. The population was much smaller, everyone knew each other... It had been so much nicer in the old town... So why the hell did he decide to move?
   Sans shrugged it off, turning around to lock the shop door before heading away from here. He knew damn well why he was so moody at the moment.
   But he couldn't openly show it. No. He had to keep it on the down-low. Otherwise, people would freak out and they'd have a repeat of what happened in the last town they'd been in.
   Poor Papyrus. It seemed he was always on the move with his brother.
   Having magic like the kind Sans had was a lot of responsibility. Sometimes, a bit too much for him to handle. The problem was, every single time he slipped up, they'd have to pack up and move again. It sucked.
   Sans sighed, pulling his hood up over his head and bundling himself up in his jacket. It wasn't even cold outside, but his instincts were telling him to stay hidden, at least as much as possible.
   The skeleton silently began walking across the street, then along the sidewalk on the other side. He moved at a relatively fast pace, since he knew what was coming and he didn't want to be in town when it struck.
   His left eye began to burn with an icy-blue inferno, causing him to pull his hood down lower in order to keep it hidden. He even closed his eye socket to prevent the glow from being visible by any monster who might be passing by.
Sans had been so focused on hiding things that he hadn't heard the police officer's voice calling from behind him.
"-Hey! Punk! Where do you think you're going?!"
The skeleton whipped around, his open eye socket going wide. "H-Huh?"
"Dude! It's like, midnight! What the hell are you doing sneaking out at a time like this?!" The officer continued as she pursued Sans. It wasn't like Sans was running or anything, so it didn't take her too long to catch up.
"Uhh... I-I'm just gettin' some fresh air, ya know? The forest is really pretty this time of year. Heh..." Sans responded, keeping his face hidden from the officer, who was now walking right next to him.
He glimpsed at her badge, noticing that her name was Undyne. "Soo, why are ya followin' me?"
"Do you have any idea how shady some monster in a blue hoodie walking down the street in the dead of night is??"
"Eh. I figured with all the edgy teenagers around here that you wouldn't think it's unusual," Sans muttered, keeping his head down low.
"Well jeez dude, can you at least take the hood off? I can barely understand what you're saying," Undyne asked, reaching over to pull off the hood.
Just as she was about to do it, however, Sans jerked his arm up and grabbed her arm, preventing her from taking the hood off. "Don't."
Undyne gave a slightly confused look. "What's your deal?"
Sans inhaled deeply before answering. "None of your business. Good day, Officer."
Without another word, Sans picked up the pace, pulling ahead of Undyne in his determination to get away.
Undyne snorted in disbelief, taking off after the skeleton. "Hey! I don't appreciate the attitude, punk! Get back here!"
Sans paused, taking a deep breath before turning to face her. "Listen. My damn attitude is the least of your concerns right now. Maybe you should be more worried about the traffic jam you caused earlier."
"I didn't cause that traffic jam, okay? Those dumbasses got in my way!" Undyne insisted.
Sans chuckled. "Well I hate to break it to ya, but that ain't how traffic works, buddy. Now, if you'll excuse me, I've got some important matters I need to attend to."
He didn't even wait for a response before he ran off, heading into the forest before Undyne could follow. He didn't even bother looking back to see if she'd followed him or not. Things were building up too fast. He was running out of time. He'd been stalled for long enough.
But sure enough, Undyne's curiosity got the better of her, and she followed. She was careful to step lightly, fearing that the fallen leaves scattered across the ground would make too much noise, alerting the skeleton of her presence.
   The forest was rather beautiful this time of year. The leaves on the trees were all different colors, ranging from crimson to golden yellow. Each delicate patch of color was brightly illuminated by the light of the full moon, adding to the serenity of the peaceful autumn woods.
Soon, the skeleton slowed to a halt in a large clearing, one that Undyne didn't even know existed. To be fair though, she hadn't done too much exploring in the forest. She didn't know half the stuff that lied within them.
"This'll do..." Sans muttered, surveying the area with a rather weary expression on his face.
He sat down in the center of the clearing with a sigh, his back facing Undyne, who was watching closely from behind a tall oak tree.
   "What's he doing?" Undyne murmured softly to herself, narrowing her eyes in suspicion. "Did he literally just come out here to sit and stare out into the forest?? That's lame."
   For a moment, that seemed to be all he was doing. But after a few minutes, something began to happen. Just as Undyne was about to give up and go back to town, Sans let out a pained grunt, doubling over while clutching at his wrist.
   Undyne's attention was drawn back to the skeleton at the rather peculiar sound. What the hell was going on with him? There was literally nothing around that could be hurting him. Unless...
   "God damn... Is he hurting himself?? Why the hell would he drag his ass all the way out here to do that??" Undyne commented, keeping her voice quiet, as not to inform the other monster of her presence.
That was when she became aware of the sound of bones cracking. It seemed to be muffled by something, but it was distinguishable nonetheless.
It took her a moment to realize that the sound was coming from the skeleton. God, it made her sick just thinking about it.
"C-Come on, dude... D-Deep breaths... You can d-do this... Th-This is nothing new..." Sans mumbled under his breath, which was coming in short, ragged gasps.
"Oh god... What's happening to him??" Undyne whispered, her heart pounding in her chest.
   Sans let out another grunt, falling forward onto the ground as his grip on his wrist tightened. Claws were beginning to form on the tips of his fingers, which were digging into his sleeve, puncturing the fabric and stabbing into his forearm.
   He inhaled sharply between his teeth, which were rapidly growing sharper. His body began to shudder uncontrollably, his bones rattling as a result.
   Undyne wasn't sure what to think of the situation. In all her years on the police force, she'd never encountered something quite like this. She hadn't even heard of anything like this.
   She was pulled out of her thoughts by a loud crack, followed by a series of dry snaps, which drew her attention back to the skeleton, who was moaning in agony.
   She barely muffled a gasp as she saw what was happening. Something seemed to be protruding from along Sans's spine, causing a ridge to form along the back of his jacket.
   Undyne had to slap a hand over her mouth to keep herself from exclaiming as the skeleton's jacket finally tore, revealing several massive spikes that had somehow emerged along his vertebrae.
   None of this was right! Monsters weren't supposed to shapeshift! They had one form, and they stuck with it!
   Undyne found herself regretting following Sans out into the woods. If she'd just left him alone, like he told her to, she wouldn't have had to witness this!
   She heard the sound of bones cracking and fabric tearing once more as more spikes shot up from the skeleton's shoulder blades and elbow joints, causing him to cry out in pain.
Sans suddenly collapsed, his legs splaying out behind him as he clawed at the ground almost desperately. His legs were beginning to change; his feet elongating and the tips of his toes growing sharper, piercing through his worn-out slippers.
The entire structure of his legs were shifting and reforming, changing rapidly from a normal plantigrade structure to a more digitigrade appearance.
Undyne couldn't help but cringe with every cry of anguish the skeleton made. His voice was slowly beginning to change as well, getting deeper and raspier with every increasingly raw, feral scream that escaped his mouth, as well as becoming slightly double-toned.
The chilling part about the sound of his voice wasn't necessarily that it was so unnaturally deep and rough, it was that the skeleton's actual voice could still be faintly distinguished beneath the voice of the creature he was rapidly becoming. It was almost as if he were being trapped and held hostage by the beast inside of him, and this was his cry for help.
A tail had somehow grown out from the base of his spine, lashing out behind him like a whip. The skeleton had started clawing at his head as it began to shift as well. Massive horns emerged along the back of his skull as his face stretched out into a long muzzle. With a loud crack, his skull split open from his nose socket to his forehead, causing Sans to scream in agony.
Undyne had become so focused on the individual changes that she hadn't noticed the mass that Sans's body was rapidly drawing on. His ribcage had begun to expand, tearing through what was left of his jacket and t-shirt. Every bone in his body was distending and thickening all at once, each new crack and tremor bringing on a fresh wave of pain, and a loud wail of anguish to go with it.
Eventually, after what felt like ages of torture, the transformation ended, leaving Sans laying down on his side in the middle of the clearing, breathing heavily.
His breath rumbled strangely in his throat as he closed his eyes. Changing forms always tired him out. He felt as though he could sleep for a week.
Undyne didn't know what to do, or even how to react. She'd just witnessed a monster completely change forms. She didn't even know if he would be friendly or not.
"I'm not gonna take chances," She growled softly, slinking closer to the edge of the clearing, summoning a spear in her hands.
Sans's head snapped up, aware that someone else was nearby. He let out a soft growl, shakily rising to his feet. He scanned around the edges of the clearing, his left eye glowing ice-blue in the darkness and illuminating his massive form.
Undyne crept forward just a bit more, staying as low to the ground as she possibly could. As much as she wanted to deny it, she was outright terrified of what stood just a few yards away.
The large skeletal beast arched his back slightly, his tail flicking back and forth idly. "I know you'rre therre."
Undyne flinched at the sound of his voice. It wasn't even recognizable as the same skeleton she'd spoken with barely a few minutes ago. There wasn't even a hint of his real voice beneath the deep growl anymore.
She closed her eyes, taking a few deep breaths before suddenly charging out into the clearing, spear in hand. Sans backed away, a look of fear in his glowing left eye.
"Listen. I don't know what the hell you are, but you sure as hell aren't gonna hurt anyone. I'll make sure of that," Undyne snarled, crouching down into a battle stance.
Something snapped in Sans's mind at that moment. The control that he'd kept such a strong hold on began to slip from his grasp. He continued to back away, growling quietly in an attempt to warn her off.
But it was no use. She wouldn't back down. She just remained poised, ready to launch an attack at him at a moment's notice.
Sans clawed at his skull with one hand as he desperately fought against the influence of the beast. But no matter how hard he tried, it was a war he was slowly losing.
His vision became clouded with a red haze as he began to lose control. He squeezed his eyes shut for a brief instant, and when he reopened them, they were both burning with intense blue light.
"Come on, punk! Just fight me already! I've been needing some action in my day!" Undyne shouted, a wide-toothed grin spreading across her face.
She couldn't help it. Her underlying ambitions were taking over. She'd waited so long for something exciting to happen. Directing traffic was so goddamn boring!
The beast's pupils dilated to slits, giving his eyes a distinct cat-like appearance. Blue smoke began to pour from his maw as he advanced towards Undyne, a rumbling growl echoing deep within his throat.
Undyne quickly realized her mistake, and flinched back. Sans just kept moving towards her, his massive form looming over her and striking fear into her heart. She found herself frozen to the spot, unable to think of any way to take action.
The glowing spear in her hands dissipated as she backed down. But it became very clear that Sans would not be stopping any time soon.
It wasn't long before he was towering over her, his ice-blue gaze fixated to her. He suddenly let out a booming roar, rearing up on his hind legs before slamming his clawed hands back down into the ground.
In the short amount of reaction time Undyne had, she quickly darted out of the way, barely avoiding being crushed by the force of the creature's attack.
Undyne slowly regained her thoughts, just in time to combat the enraged beast that stood before her. She narrowed her eyes in fierce concentration as she summoned her spears once more, using several to shield herself as Sans lashed out at her with razor sharp talons.
She jumped back as he slammed his forearm down barely a few feet away from her, taking the opportunity to strike at him while he was down for a couple seconds. She jumped up, bringing her spear down hard against his ribs.
He roared in fury, frantically scrambling to his feet to fight back. He lowered his head, snarling loudly as he suddenly charged at her like a ram. Undyne leapt out of the way, summoning several spears around the beast's feet.
He kept roaring in frustration as he realized that he couldn't get past the barricade of glowing cyan spears. Undyne moved forward slightly, remaining on-edge.
   "Listen, I'm sorry I pissed you off. I'm sorry I even followed you out here," Undyne apologized, hoping it'd snap the skeleton out of his anger.
   Sans snarled in response, shaking his head from side to side.
   "It's just that... Everyday's so boring, doing the same things day in and day out. I just wanted something new, and following you out here seemed like something different, y'know?" Undyne continued, regaining her hope as the beast's growls began to quiet down.
   Sans growled softly as he slowly took back control. He closed his eyes for a moment, and when they reopened, they had gone back to their normal state.
   He stared down at Undyne, a look of fear crossing his face. "Oh sshit. You ssaw everrything, didn't you?"
   Undyne shrugged, all the spears that trapped Sans disappearing. "I saw enough to make me question what the hell was going on."
   "Dammit... And we jusst finisshed moving in too..."
   "Hey," Undyne cut him off. "I can keep a secret. Plus, that was way more fun than directing traffic, or handing out speeding tickets!"
   Sans looked away. "It'ss not rreally ssomething that sshould be played arround with... I don't alwayss have full contrrol overr it..."
   "We got'cha back, didn't we?"
   Sans sighed. "I guessss. Jusst don't attack me like that again, 'kay? That'ss what made me frreak out."
   Undyne reluctantly agreed. "Fine. We'll keep this on the down-low then. And don't worry about moving out. As long as you don't hurt or scare anyone, you should be fine."
   Sans breathed a sigh of relief. "Thankss Officerr Undyne."
   Undyne grinned. "No problem, punk."

Wow! It's been quite some time since the last oneshot, huh?

Let's see... The last one was back in June?

Aww sheit. You guys have been starved for Gaster Blaster transformations for five months!

Anyway, all kidding aside, I'm so sorry it's been so long! I've been pretty busy, plus I've been fighting with some writer's block and lack of inspiration for quite some time now. :/

BUT! I finally found enough inspiration to write this! :D

Hope you all enjoyed! And until the next oneshot, stay determined!
-Sora