"ALERT, ALERT, hull breach on observation deck 2j Emergency bulkheads lowered. ALERT, ALERT, hull breach on observation deck 2j. Re-pressurising damaged compartment. ALERT, ALERT, hull breach on observation deck 2j…"

Robotnik glanced up in annoyance at the tannoy speaker as he fumbled with his helmet in the inner airlock.

"Of course there were going to be minor hull breaches; you don't bring a space station this far down into the atmosphere without losing some bulkheads to kinetic ablation!" he retorted. "And that wouldn't have been necessary if the hedgehog hadn't attacked Wing Fortress precisely when the Death Egg was on the other side of the planet!"

Wrenching his flight helmet free, Robotnik threw it violently at the airlock's control panel. He was angry. The destruction of Wing Fortress represented a crippling loss in materiel, firepower, and force deployment capacity, all at the same time. And that was before he'd personally had to endure going from 0 to Mobian escape velocity in 5.1 seconds to avoid going down with the ship.

The Death Egg's equatorial rotation had spun back up to 1g as he waited for the airlocks to cycle, and so Robotnik hauled himself out into a comfortably familiar environment of light, metal, and faux-gravity. Indeed, but for the upwards curve of the floor, it was barely distinguishable from that which he'd left behind (permanently, he reminded himself) in Wing Fortress.

"ALERT, ALERT, unauthorised personnel detected in observation deck 2j"

Robotnik blinked.

"What?" he asked, incredulous. An intruder? Here? Preposterous!

"…precise nature of the gold rings is something else worthy of additional investigation. The most obvious point we can make about them is their profound biomedical properties, as the blue hedgehog has forcibly demonstrated on countless occasions. The rings can apparently undo recent musculo-skeletal damage, and possession of even a single specimen precludes the lethality of all but the most egregious of injuries.

This on its own is proof that they serve as more than mere biological curative. The vast range of injuries upon which the rings can act, from simple puncture wounds to gigawatt muon laser irradiation, precludes a classical mechanism of action. And then there's the injuries they won't work on: crushing, drowning, explosive deceleration… consult the autopsy reports for Green Hill subject batches 9.210/j through 9.210y inclusive for full details.

No, indeed, the truth is far more intriguing. The rings don't cure the injuries; they prevent them from ever occurring, retroactively. One example of particular interest was Green Hill subject 9.189/e-11; a squirrel, sciurus mobius. Over the course of the experiment 9.189/e-11 was decapitated using a torque method a total of eight times, with absolutely no ill effects provided the creature was infused with at least one ring. Indeed, multiple rings seem largely redundant as far as surviving injury is concerned. High-speed recording of the incidents showed the subject flicker momentarily, and during these periods they seem impervious to further harm. No matter how many times the specimen's head was removed, it would reappear attached to the neck, without crossing the intervening space, and with no scar tissue, no myoclonic jerking, nothing on the subject's body to indicate that the decapitation event had even taken place. Annoyingly, 9.189/e-11 became profoundly distressed and avoided the ring on the ninth trial, making the decapitation permanent.

On the other hand; destruction by crushing force was not survivable through possession of a gold ring. This is not so much a distinction born of the type of injury, but rather the complexity, and this demonstrates the mechanism by which the rings act. Thermodynamic calculations indicate that the rings are finitely negentropic: they can retroactively negate injuries, but only of a limited disorder.

Where the negative entropy actually comes from is unclear. The 'flickering', previously described no doubt has some relation, but at the same time it seems to knock the subjects into a phase-state whereby they interact more weakly with standard matter, enabling them to transmit through restraints in many cases. This necessitated rather specialized experimental methods. To this end, in efforts to quantify the nature of the strobing, subjects 9.210/u-04 through 9.210/u-56, all bluebirds, sialia greenhillus, were, with an attached ring, subjected to impalement wounds of varying severity. The subjects suffered a causally rate roughly proportional to..."

A white glove crept over the exposed control panel, by chance grazing a button which turned off the Doctor's grim recording. Groaning painfully, Sonic levered himself out of a layer of plexiglass shards. Gasping breaths drew sweet oxygen into his ragged lungs, and the high-pitched whine in his ears gradually faded, to be replaced by the familiar sound of Robotnik's alarm clarion. It would almost be comforting, if not for the promise of approaching robotic murder.

What had once been observation deck 2j had become, quite literally, a crash site. Although Sonic's speed has smashed through the vacuum-sealed window, emergency decompression bulkheads had slammed down only a second later, preventing the hedgehog, the glass shards, and most of the air from being sucked straight back out into the cold of space. The whole scene was painted crimson by the emergency lighting, and as Sonic propped himself up against the wall, he was thankful for that; he didn't really want to see how much blood he'd lost to the carpet of shards. It felt like a lot.

Glass crunching underfoot, the hedgehog staggered towards the door.

"Why are you still not dead yet, hedgehog?" Robotnik snarled at his screen. The display showed Sonic, bruised, limping, and weary, but nonetheless advancing through the Doctor's most delicate and important laboratory complexes. The only consolation Robotnik could take was that Sonic refrained from actively smashing the place up; but all the equipment would have to be gamma-irradiated to purge contaminants, and that would kill the painstakingly-cultured biological warfare agents...

Still, not much longer now. Gripping a screwdriver between his teeth, Robotnik plunged his hands into the tangle of wires he'd exposed beneath an auxiliary control sub-router, and began reconnecting electronics with the kind of alacrity afforded only to the very mind who had designed and built the system. The Death Egg was one giant machine; it was the Doctor's home turf, and he intended to demonstrate that to Sonic in the most fatal manner possible.

Rewiring with one hand and reprogramming with the other, Robotnik glanced back at the monitor. Sonic was picking up speed and confidence even as he moved through the low-g workshops. With a start, the Doctor realized that Sonic was only a few rooms away from his own location underneath the auxiliary bridge!

Robotnik spat out his screwdriver in frustration; it cartwheeled lazily in the low gravity before bouncing off the cable-strewn floor with a clang. What kind of dumb luck had brought the blue menace here!? And this quickly? He hadn't finished bypassing his own safety protocols yet – he needed to at least slow the hedgehog down, if only for a few minutes.

As on Wing Fortress, the Doctor ran through Death Egg's inventory in his head. The station was almost completely defenseless internally; "One hundred kilometers of space between it and the Mobian surface should be quite sufficient a defense!" he muttered bitterly. Nonetheless, some of his most advanced weapons prototypes were under development here; perhaps they could be pressed into service… prematurely.

Allowing himself a wicked grin at the clash he was about to instigate, Robotnik tapped out a new series of commands.

DEATH EGG WEAPONS LAB
Command I.D.: DE m3897/10.c
Timestamp: MY10.363 - 90.09.37
Emergency Bootup: Project Metallix, Unit 01
Authorization: Dr. Ivo Robotnik

Sonic wandered unsteadily through the spotless chrome labs, casting his eyes over the unnerving array of humming machines that packed the spotless rooms. Their functions were in most cases utterly obtuse to him; others, he could hazard an unpleasant guess. There are only so many reasons an operating table would need heavy metal restraints and sluices.

The pain in Sonic's lungs had begun to recede – from flaring, near-black-out levels whenever he drew a breath, through simple agony, and now just as though he'd swallowed a few of those shards of glass while he was passed out in observation deck 2j. For all he knew, he had, but now really wasn't the time to contemplate exploratory surgery. Sonic was resilient, and as he looked around the lab, his injuries seemed trivial compared to what his fellow Mobians, his friends, must have suffered in here, and in Robotnik's other secret labs down on the surface of the planet.

In some ways, Sonic hoped Robotnik enjoyed the experiments he performed; hoped the Doctor had cackled with malicious glee as his subjects were cut or burned or electrocuted at his whims. But he suspected that it hadn't happened like that. Conventional psychotics took pleasure in the deaths they caused because they valued life, and taking it away was an assertion of power. Robotnik… no, Robotnik was different. He didn't enjoy the fact that thousands of thinking creatures had died in his experiments; died in terror and pain and loneliness, far away from their home zones and their families. No, he didn't enjoy it. Because he simply didn't care.

And if anything, that was worse. To Robotnik, the Mobians were truly beneath contempt. Their lives were totally valueless to him; they were simply the means to an end, to verify or disprove one of his precious theories, their entire existance reduced to a single data-point on some graph that only Robotnik would ever read or understand.

A cold fury rose in Sonic as these thoughts swam in his head, the hatred pushing aside such trivial things as his own personal pain and exhaustion. He would find the Doctor, and he would make him pay.

In general, one found Robotnik simply by smashing his badniks until the Doctor decided it was time to personally enter the fray. But Sonic hadn't seen a single defender since his arrival, leaving the hedgehog somewhat at a loss. An open doorway marked 'Weapons Testing' led out of the labs, and, wanting to leave the macabre operating table behind him, Sonic ambled through the awning.

The first indication Sonic had that something was wrong was a faint whirring sound as he crossed over the threshold. The labs had been illuminated by pale blue light reflected from Mobius' dayside, but there were no windows here, and as Sonic's eyes struggled to accustom to the dim lighting, the door swished shut behind him. Meanwhile, the whirring noise increased; it was a sound like a circular saw-blade revving to life.

When the attack came, it was all Sonic could do to lurch out of the way and avoid being instantly bisected. A grey blur whipped through the space he had been standing in milliseconds before, the turbulence of its passage twisting Sonic around and driving him to the floor, knocking the air out of already-damaged lungs.

Flipping himself over, Sonic stared up at his adversary as it skidded to a halt and turned back to face him. His eyes widened in horror.

Ever since Sonic had first encountered Robotnik's badniks, ever since he has seen how the Doctor trapped captured creatures inside cauls of cold steel, wired up to the robot's internal mechanisms, he had nightmares. He dreamt of a mechanical version of himself, of being dragged into the terminal embrace of those internal wires, of seeing a robotic ribcage snap shut behind him, imprisoning Sonic forever inside a walking crypt.

The metal Sonic was there, as if plucked straight from the darkest recesses of his mind. It towered over him by more than a meter, all angular panes, sharp edges, and steel grays. Cruel, serrated spines punctured out of the robot's back, their blades in constant motion: the source of the ear-piercing whirr. Its eyes were coal-black, with baleful red irises glowing in the half-light.

The rockets in its feet flared, and the robot launched itself at Sonic again.

A savage smile took form beneath Robotnik's immense moustache as he watched the battle. Sonic and his metallic counterpart threw themselves at each other again and again inside the adjacent room. As the monitor showed the blue hedgehog being slammed into the wall, Robotnik imagined he could feel the force of his impact, despite the many layers of shielding built into the weapons testing compartment.

With one eye on the battle, he nonetheless continued his work modifying the airlock protocols. When he had designed the Death Egg, it had been imperative to ensure that the various airlock doors simply could not be induced to simultaneously open to space. The results would be catastrophic, on this or any other space platform – opening both doors to vacuum would suck everything that wasn't nailed down (and probably a hefty chunk of the things that were) out into space. His experiments, his weapons, even the Doctor himself if he'd had the misfortune of being in the wrong compartment when it happened. So it was an elementary tenet of space engineering that should be no way one could open the inner and outer airlock doors at once.

In the present situation, however, that was exactly what needed to happen. Robotnik had been tampering with the hardware and software of the airlock controls for the last eight minutes, and was almost ready to flush Sonic out into space in the most un-ceremonial manner possible. His fingers were a blur as he tapped out commands, tailoring computer codes to evade the firewalls and safeguards he himself had programmed years earlier.

The Doctor glanced at the battle once again. He even allowed himself to hope that Metallix, the metal Sonic, would defeat his flesh-and-blood opponent right now, to save him the trouble of ejecting him into space. Despite the fact that it was only a prototype, a work-in-progress, the metal hedgehog was still a savage killing machine, considerably more resilient than a regular badnik.

At the moment, however, neither hedgehog seemed to be getting the upper hand. Sonic was bloodied but not beaten, and inevitably had the edge in speed over his mechanized opponent. Metallix had the ability to inflict massive damage with his chainsaw spines, but if they never connected, the weapons were irrelevant. Mirroring his counterpart's injuries, one of the metal Sonic's ruby pupils had winked out, the black sclera around it visibly cracked, and electrical discharges arced sporadically from the robot's damaged right shoulder.

The Doctor turned his attention back to the airlock mainframe. An impasse was all he needed. If the machine could hold Sonic at bay for a few more seconds, the reprogramming would be complete, and the eventual result of the battle would be irrelevant. Just a few more safeguards to circumvent…

THUNK.

Robotnik defiantly felt that one, even through the shielded wall. One of the combatants had just been thrown against the side of the testing room with immense – and unambiguously fatal – force.

And it wouldn't even matter if it was Metallix. The modifications were complete. Right now, with a single keystroke, he could open the adjacent compartment to space, and send Sonic tumbling to a painful, decompression-induced death.

Robotnik turned to the screen, his face beaming with the certainty of his own triumph.