Commission for  Sg~, not usually a sonic fan but this was thoroughly enjoyable to write out.

Eggman has plans for our furry hero, and they involve a rather... vicious alternate form for him.

Wolf serum

“Unnnghh…” Sonic groaned as his head throbbed into consciousness. He felt like every blood vessel in his skull was swollen and pulsing all at once, a mass of grimy pain that had him wincing as he tried to stand up. Colours swirled in his vision as he cracked open his eyes, the familiar steel greys of metal bars mixed in with vivid red. As he staggered to his feet he started to look around and notice the strange laboratory he was caged in. Around him gigantic vats of liquid glowed eerily, bubbles slowly pushing through the goop and bursting at the top, and nearby tesla coils sent arcs of electricity crackling through the air. It was exactly what he’d expected a mad scientist’s laboratory to look like, and as he looked up he realised that the mad scientist in question was none other than Dr Eggman himself.

“Wakey wakey, little hedgehog! Gahahaha!” that grating voice snapped Sonic to attention, and he looked up to see a familiar handlebar moustache peering down at him. “You might be fast, but my machines are faster.”

“Urgh, yeeeah I doubt that.” The hedgehog shook his head as he began to look around the cage for any weaknesses, any point that he could exploit to slip out. He was out of luck though - Dr Robotnik was a thorough man, and his cage had absolutely no way out besides flat out breaking the metal bars. “What do you want with me, I don’t have any chaos emeralds! And if you think Tails is gonna -”

“I don’t care about your silly little friends. Not when I have...this!” Eggman fumbled for a few seconds before pulling out a crimson gem. He held it aloft triumphantly, a glowing red light in the darkened room. “Unfortunately I’ve thus far only managed to locate this one, but that does not matter. One is all I need.”

“For what?”

Sonic gulped as Eggman cackled, before going over to the side. There was something large underneath a tarp, and as the doctor pulled it away he revealed it to be a gigantic vat of what looked like goo. Clear, viscous liquid bubbled gently, globs of air languidly floating to the top before bursting in pops that he could almost hear through the thick glass.

“Nanites, suspended in a liquid compound. The trouble is powering them, with each nanomachine the energy required to power it is enormous compared to the machine itself - multiply that up and you need fairly insane amounts of power to even make them work. Of course, I never had a power source strong enough. That is until now.” Eggman opened a hatch and deposited the chaos emerald into the vat, where it quickly sunk out of sight. However almost immediately swirling tendrils of red began to streak through, and after a few seconds the entire vat glowed an ominous scarlet. It almost looked like the mixture was squirming, moving a little more than normal.

“W-what the hell!” Fear gripped Sonic as he watched Eggman pull out a syringe gun and extract a small amount of the liquid, tapping it to remove the air bubbles.

“Restraints!” Eggman barked, and robotic clamps sprang from the floor and grabbed Sonic, holding him in place. The doctor walked closer, deliberated for a moment as he chose a spot, and then stuck the syringe gun right into Sonic’s arm. The hedgehog yelled as he felt the liquid enter his bloodstream, struggling against the metal clamps. The substance was thick and greasy, like honey flowing through his veins, and worse than that it was cold. He could feel it permeate every inch of his body, pumping through his heart and up his neck, until it reached his brain. Trembles wracked him as the clamps retracted and Sonic fell to the floor, hugging his sides.

The first signs of change came from Sonic’s teeth, which began to sharpen with a sound like chalk grinding on a blackboard. He grunted as the first pulse of pain went through his system, a prickly heat that lingered a little too long to be comfortable, and then grunted again as it echoed back through him stronger than before. He could almost feel his cells changing, his body setting up for the changes to come.

“What - Hrrr - what did you do?”

Eggman laughed from afar. “I’ve always held particular interest in your… nocturnal transformation. The were-hog, I believe you call it. Well as you might have noticed, it’s the night of a full moon.” he gestured to a nearby window, where sure enough the moon was full and round in the sky. “So these nanites are going to enhance your transformation and rewire the synapses in your brain, making you my powerful servant. With you by my side the other emeralds will be easy to obtain! Gahahaha!”

Sonic yelped as his body twisted at an awkward angle, as pressure mounted and held, and held, and held -

SNAP[/b]

Howls of pain filled the air as his bones shattered, almost immediately beginning to reform as hordes of tiny machines knitted the calcium back together in a more fitting arrangement. Most of his bones grew longer this way, extending from his frame and removing his previous stocky build. Now he was proportioned more like a human, evened out, although he retained the thin limbs of his old body - the bone had grown but the flesh and muscle had not caught up yet. He would have looked at his body in horror but already he could feel an alien presence in his head, holding his neck in place. No, there were….two presences. There were the nanites, cold rows of logic and orders and neat, perpendicular lines, but there was something else. Sharp, jagged, messy, clawing at the darkest recesses of his mind. He growled in pain, and this time there was more in it - the corners of his mouth curled up further, his body tensed up, his lungs emptied a little further. Sonic shook his head to try and clear it, but alas he was the battlefield for two opposing forces, and he was losing on both fronts.

More snaps, these ones not as aggressive as the smaller bones broke and reformed. He panted at the sensation but it wasn’t as sharp as before, the pain was dulled. He became aware of a burning sensation all over his body, like his muscles had been dipped in lava, and as it got hotter and hotter he noticed what it was.

His muscles were slowly expanding, rippling with newfound strength as he bulked up. Great slabs of strength welded themselves to his arms and legs, shaping themselves into biceps, quads, lats - anything they could. All available space was taken by mass, and thanks to his stick-thin build there was plenty to work with. It would have been pleasurable had it not been for the heat - there was a strange thrill in the way he felt his strength soar, in how his body grew both lighter and heavier at the same time, more mass but equally more strength to wield it properly. He could almost feel the momentum in his frame as he leaned through the air, long curves appearing on his arms and legs where there had been nothing before. He would never be big - the dose he had been injected with was too low for that - but with just a fraction of a chaos emerald flowing around his body he was looking far more athletic than before. It was while he swished his arms and legs through the air that he realised the quality of his fur was changing, his usual short, clipped style growing outwards with a feeling like intense pins and needles. He watched as it flowed across him, a strange shaggy mane that only accentuated his body with each movement. He could see the muscle even underneath the canine fur, sculpting the shape of his body into something more powerful, more appealing. Toned, that would be the word to describe himself - a toned anthro wolf.

Wolf?

It was true, he realised as he looked down at himself. He still had his quills, and he hadn’t grown enough to burst out of his familiar trainers and gloves, but other than those two factors he could have been mistaken for a stocky wolf, one that went to the gym a little more often than most. His strength was disproportionately higher too, and as he flexed an arm and watched the bicep rise he could almost feel the power coursing through the muscle. Oh, he loved looking at it, he could just imagine ripping through flesh like butter, carving those claws through skin and bone….

Sonic shook his head as violent thoughts seared through his skull, framed with instructions to obey and cease resistance. His mind was not his own, he could feel that spiky presence getting stronger, making him angrier and more aggressive. He didn’t just want to capture Eggman, oh no, he wanted to rip him apart. He wanted to feel the doctor’s body give way under his strength, and only when he was begging for mercy at the werehog’s feet would he finally grant Eggman the mercy of death. He would swipe through his neck and watch the blood sing through the air –

“Obey! Obey damn you!” Eggman shook his remote, slapping it repeatedly. “The transformation is done, you should be completely mine now! What’s happening?”

“You thought that would work on me? Muahahaaaahahrghhhh!” Sonic’s laugh was a far cry from his usual humorous chuckle. This was long, sinister, full of promises of violence and malevolence.

Now it was Eggman’s turn to feel fear. He backed away from the cage, still pressing buttons on his remote. Sonic could feel every button press in his head as an order, the nanites that had incited his change still trying to make him obey, but it was too late now. He grabbed the metal of the bars and strained, feeling those arms fill with blood and power as the metal creaked. Slowly the sound of screaming metal filled the air as he began to bend them apart.

“That’s impossible! Computer, get me the emerald!” Eggman frantically went over to the tank and pulled out the jewel, wiping the last dregs of red sludge from its crystalline surface. The moment it was pulled out of the liquid it began to fade back to a dull grey, the energy quickly dissipating without a power source to keep it going, and Eggman stowed it in his pocket. “Lock down EVERYTHING! Prep the jets, wipe the hard drives. Sonic doesn’t leave this room!” He quickly ran as Sonic bent the bars further, his claws digging worrying gouges into the metal as he snarled and strained, and just as he left the room the sound of shearing metal snapped through the air. Sonic burst from the cage, howling angrily as he looked around for his tormentor. He was just in time to see a large metal door slam down behind Eggman, blocking off the exit. The pumped-up werehog ran to it and sent a fist flying into the metal, but while it dented and buckled it still held no matter what he put into it. He wasn’t strong enough, and the thought teased him, it tormented him. He needed more, more strength, the strength to rip apart his foes and crack their skulls…

And as he looked back at the liquid of the vat, he realised he knew exactly how to get it.

As he approached the tub he could see that the red light was still fading, but over half of it was still powered. The tap to get it out was all the way at the top, but that didn’t matter - he didn’t plan on moderating himself after all. Just a bit more strength was never going to be enough, he needed ALL of it. He would be more than just a beast, he would be a god, a monster, a deity all rolled into one snarling package. He could see himself in the reflection of the glass currently, and truth be told he liked what he saw. Honed muscles bumping out from all angles, a well-defined chest that stuck forward just enough to be impressive, a tapered torso that led down to a nice, sharp six pack. Legs that were long but still somehow stocky, arms with thick biceps and triceps sticking out on both sides, shoulders like cannonballs. Everything was good, but he couldn’t help feeling that it would be so much better with more.

With a grin and a snarl, he wound back and smashed a fist into the glass, shattering it and causing the liquid to pour all over him. It was much thicker than he first thought, almost like heavy syrup gliding down towards the floor, and he opened his mouth to catch as much of it as possible. It wasn’t as potent as before, but as he swallowed it he could feel the new nanites linking up with the old, charged ones already in his bloodstream, the tiny machines exchanging lightning-fast protocol handshakes before sharing energy between them. There was so much of the stuff that he thought he was going to choke on it, but he loathed to let even so much as an ounce of the stuff go to waste. Already grey globs were seeping into the floor, the majority of it splashing around him and slowly melting away, but he didn’t care. He used his new strength to hold his ground against the tide of liquid, swallowing over and over until the stream drained into a trickle, and he was left there soaking wet and panting heavily.

Sonic felt the changes after a couple of seconds, enough time for the nanites to orientate themselves. It was different this time, like someone had struck his skull with a hammer, a shock of power that ricocheted around his insides. Except it wasn’t accompanied by that strange, ordered control like before - Eggman had evidently abandoned his remote, or perhaps he was out of range. Either way there was nothing restraining him now, and he could feel them at his command. They were waiting for an order, so he gave them one.

“Bigger.”

Immediately a rush of strength blasted into him, his heart kicking up a notch as every nerve flared with energy. He was half expecting to just explode with new strength with how it felt, but no; like before the growth was preceded by hideous cracks of bone, howls of pain filling the air. They were worse this time, a consequence of his stronger frame needing more energy to break, and each broken bone sent vibrations rolling through him. However his pain tolerance was much greater than before, and instead of painful howls he merely grunted and grinned, safe in the knowledge that this was only the beginning, this was the prequel to the power he desired. The bone growth only lasted a short while, and by the end of it he noticed he was taller, much taller than before. Before he had barely pushed 6ft tall, but now he was closing in on 9ft, evenly proportioned and still vaguely athletic. His muscle definition had lost some of the pop due to being so stretched out, but he didn’t care. He rolled his neck, feeling the bones quite literally crack and snap as they reformed stronger, cradling his head in reinforced armour.

Then the growth began.

It was like someone had stuck a jumper cable into his back and lit him up with electricity. Great gouts of power surged into his body with the force of a thunderstorm, crackling down his spine and forcing him onto one knee. The strength, oh the strength, the power….[/b] Sonic felt his mind slip further away as power sang an intoxicating song in his head, as that other presence grew darker, spikier, larger. Instead of recoiling from the painful heat now he began to lean into it, embracing the agony of change, of improvement. He held an arm out, grinning madly as the bicep swelled with power, new muscle winding over the old and melding seamlessly into the arm. He flexed it, laughed as the bicep detonated higher than it ever had before, then laughed harder as it stayed there instead of deflating when he unflexed his arm. Similar things were happening all over his body - he tensed his thighs, clenched his chest, stretched and constricted various parts of his body, and all of them were stroked with growth when he did. Some of the constriction came not from his body but from his clothes - his gloves were already showing tiny holes in the ends where his new claws had pierced the tips, and his shoes felt uncomfortably tight to the point of being almost painful. He had already doubled his previous body weight, achieving his previous build but on a body 2ft taller than before, but it wasn’t anywhere close to stopping yet. Sonic gasped as it grew even hotter, more power packing in and forcing him outwards. As he began to swell into bodybuilder territory what he noticed more than anything was his range of movement, or rather the changes in it. He could feel certain movements become more difficult, the angles of his body going from acute to obtuse, but none of it mattered. All that it meant was that he was stronger, and that was all that mattered. He welcomed the tightness, the tension, the feeling of every muscle quite literally on fire. It was his ascension, and he would not shy away from it.

His body was straining now. He had tripled his weight by now, giant chunks of muscle and sinew bulging across his mighty body, levering his arms with frankly ridiculous force. He looked like he had been hewn out of solid marble, such was the density and definition of each muscle group. Everything was picked out in impossible detail, because everything was overdeveloped. He was a menagerie of excess, and yet it all balanced out. He was just...big. So very, overwhelmingly big.

It wasn’t enough. It was never enough.

Some part of his mind was screaming for him to stop, but it wasn't in control anymore. Now there was nothing but the beast, wild and primal, and it desired even more power. As that burn started again even he winced in pain - it was sheer agony, as though fire ran through his veins instead of blood, and he could feel tendons begin to tear from the stress of holding so much power in one body. No physique was ever meant to be beyond what he was now, and yet as he closed his eyes and grew even larger, he was proving it to be possible. Sonic knew instinctively that he had already passed his body’s limit, that the further he went the higher the risk of damaging himself, but he wasn’t about to stop now. He howled triumphantly as even more power was stuffed into his body. Every muscle strained into enormous balls of strength, every limb was assaulted by power until his arms and legs were like thick, bulging trunks of flesh. His chest shot forward so far he could barely see around it, his pecs wide and full above an 8-pack that looked like baseballs shoved just underneath the skin. Even his obliques and stabilising muscles were straining, his stance perfectly still as he snarled with each pulse of growth.

As he reached a new level other changes made themselves known. This far away from his original body he was looking distinctly wolf-like, and as he approached almost a ton of muscle his quills began to melt into each other, individual spines looking like fur around his neck. Even more fur sprang into existence, shaggy reams of it sprouting from every orifice and lending him a primal, savage look to his appearance. A tail sprang from his backside with a quick jolt of pain, swishing through the air and just barely touching the steep valleys of his back. He howled as his gloves finally ripped apart, claws shearing through the fabric as if it were tissue paper, sending what looked like white confetti floating gently to the floor. As he stood there the last few identifying features of his species were wiped away, and in their place were the signals of a wolf. The tail, the mane, the eerie howl - it was all there, albeit packed into a body that could happily walk through a brick wall.

Sonic was in another world, one that felt far lighter and more fragile than he had first realised. As he caught his breath and winced from the extreme pain crashing through him, he realised just how much of a monster he was. Whereas before he had looked like a relatively toned wolf, now he was a 9ft tall hulk of snarling fur and bulging muscle, an unstoppable force of nature that ripped through the world rather than walking through it. It wasn’t just the sheer size of him - although admittedly he was monumentally large - but also the solidness. Looking at him there was not an ounce of weakness anywhere, there were no gentle shakes or wiggles of imbalance, no slight quivers of struggle. He stood as still and as immovable as a sequoia tree, no muscle even close to straining while holding himself up. His strength was disproportionately greater than even his titanic body, and he knew it. It was written all over him, in big red letters that screamed power. Looking at him now incited a sort of primal fear, that ancient part of the brain responsible for your safety looking at him and immediately raising big red flags. This was not something you could fight. This was not even something you stop.

But as much as he wanted to stand there and admire himself all day, he had things to do. He might have been at the limit before, but his new body came with stronger muscles and tendons, and more importantly a higher pain threshold. The goop had all drained away, and while there was plenty more around him he knew it was useless without Eggman’s chaos emerald. He would find him, rip the emerald from his broken fingers....there would be no holding back anymore, not now. Now there was nothing but the monster, but the strength. He would be the storm, the lightning strike, the monstrous rage that tore through his foes, the incomparable force.

The entire lab shook from the first blow, dust falling from the ceiling. The metal door must have been half a meter thick, but the first punch went straight through, buckling the metal like tinfoil. Another punch that Eggman felt from halfway across the facility, the scientist tripping over from the shaking.

“What the hell? How strong did he get?” He got to his feet, checked the chaos emerald, and that was when he heard it. A third thump, apocalyptically loud, and a howl. Not a human howl, not even that of a werehog - no, this was the howl of a wolf. This was the howl of a predator, and he realised with a gulp that he was the one being hunted. He could feel the vibrations reverberating down the corridors as whatever monster was chasing after him got closer. Sonic wasn’t even bothering to follow the corridors anymore, he was simply shouldering his way through the metal walls like a furry bullet, the sheet metal offering all the resistance of paper as he snarled and grunted. It felt good to put all that strength to good use, but he knew it would feel even better to unleash it on Eggman. He was singularly focused on the emerald, unwilling to simply halt at his current level, and even the beast recognised that he would have to keep Eggman alive if he wanted more of nanites, and subsequently more of the power that he so craved. But as he burst through yet another wall in a shower of metallic sparks and screaming metal, he knew it would be hard. At this level it would be easy to break the fragile human body, to shred it, destroy it, rip it apart –[/b] No, he couldn’t. He had to hold back. He had to restrain. He had to grow larger. He had to be bigger, to be stronger. That was his life! That was his world!

Eggman fell over as the wall beside him blasted apart, as if a bomb had gone off in the other room. He stared in amazement at the 9ft ball of muscle and fury that skidded out of the hole, colliding with the opposite wall and leaving a sizeable dent before collecting itself and approaching him menacingly. There was nothing left to indicate that this had once been a hedgehog - it looked like about 10 wolves packed into one gigantic body, throbbing with strength. Those eyes glowed crimson as it snarled and walked closer, fixated on his pocket, on the emerald.

Eggman closed his eyes and hoped the monster would be gentle. He maintained the thought up until the first screams rang out. By the end of it Sonic would have the emerald, the nanites, everything he needed to make himself the strongest there had ever been.

And he didn’t plan to stop there.