The flickering gas lamps cast long, dancing shadows across the faces of the scavenging team as they prepared to venture into the Tiergarten. It had been a week since the Citadel had officially expanded its radius of exploration, prompted by the dwindling supplies of scrap metal closer to their Berlin refuge. The Tiergarten, once Berlin's green lung, was now a blighted zone, a testament to the GCE's destructive power. Stories whispered among the Citadel's residents spoke of grotesque creatures lurking within its overgrown paths, beings twisted and warped by the contamination.

Leading the team was Stefan, a former construction worker whose brute strength was matched only by his unwavering loyalty to Marcus. He adjusted the straps of his makeshift armor, a patchwork of scavenged metal plates bolted onto a worn leather jacket. Beside him stood Anya, a wiry teenager with an uncanny knack for spotting traps and a face perpetually smudged with grease. Rounding out the team were Klaus, a nervous but meticulous mapmaker, and Greta, a hardened medic whose medical knowledge was as valuable as gold in this ravaged world.

Marcus, standing at the entrance to the Citadel's outer gate, offered Stefan a grim nod. "Be careful out there. The Tiergarten's reputation isn't built on fairytales. Stick to the established routes, mark any anomalies, and return before nightfall. We can't afford to lose anyone."

Stefan returned the nod. "We will, Marcus. For the Citadel."

With a grinding groan, the gate swung open, revealing the desolate landscape beyond. The air hung thick and heavy, carrying a metallic tang that made the back of your throat itch. Twisted trees, their branches gnarled and blackened, reached towards the sky like skeletal fingers. The once vibrant green park was now a canvas of grey and brown, punctuated by patches of sickly yellow vegetation.

As they ventured deeper, a disquieting silence settled over the team. The usual urban cacophony of pre-GCE Berlin was replaced by an eerie stillness, broken only by the crunch of their boots on the rubble-strewn ground and the rustling of unseen things in the overgrown underbrush. Klaus, clinging to his tattered map, kept his gaze fixed on the overgrown pathways, nervously consulting his compass.

"According to the old maps," Klaus stammered, "there should be a power substation about a kilometer from here. Lots of scrap metal and potentially some usable wiring."

They pressed on, their senses on high alert. Anya, ever vigilant, scanned the surroundings with sharp, observant eyes. Suddenly, she froze, her hand shooting out to stop the others.

"Hold up!" she hissed, pointing towards a cluster of overgrown bushes. "Something's moving in there."

Stefan raised his rifle, a modified hunting rifle chambered for scavenged ammunition. He slowly approached the bushes, his finger hovering over the trigger. The rustling grew louder, followed by a low, guttural growl that sent a shiver down their spines.

Then, it emerged.

It wasn't an animal they recognized. It was bipedal, vaguely humanoid in form, but its flesh was a sickly green hue, stretched taut over grotesquely deformed muscles. Its limbs were elongated and spindly, ending in razor-sharp claws. Its face was a horrifying caricature of a human face, with a flattened nose, bulging eyes, and a mouth filled with rows of needle-like teeth. It stank of decay and something else, something acrid and chemical.

The creature lunged, its claws extended. Stefan reacted instantly, firing a shot that ripped through the air. The bullet struck the mutant in the chest, but it barely seemed to register. The creature roared in pain and fury, its eyes burning with a primal rage.

"Mutant!" Stefan yelled, firing another shot. "Open fire!"

Anya and Greta scrambled for cover behind a fallen tree, while Klaus huddled behind Stefan, his face pale with terror. Greta, ever the medic, grabbed her medkit, prepared to treat any injuries.

The mutant, despite the bullet wounds, continued its relentless attack. It was fast, agile, and utterly fearless. Stefan fired again and again, but the mutant seemed to absorb the bullets with little effect.

Anya, realizing the futility of direct confrontation, spotted a pile of rubble nearby. She grabbed a handful of rocks and began pelting the mutant, trying to distract it. One of the rocks struck the creature in the face, momentarily staggering it.

Taking advantage of the distraction, Stefan charged forward, slamming the butt of his rifle into the mutant's head. The creature stumbled backwards, momentarily dazed. Stefan followed up with another blow, sending the mutant crashing to the ground.

He didn't hesitate. He knew that these creatures wouldn't stay down for long. He raised his rifle and fired a final shot, point-blank, into the mutant's head. The creature twitched violently, then lay still.

The team stood in silence, panting and adrenaline surging through their veins. They had survived, but the encounter had shaken them to their core.

"Are you alright?" Stefan asked, checking on his companions.

Anya nodded, brushing dirt and leaves from her clothes. "Just a little shaken up. That thing was... horrible."

Greta examined Stefan's shoulder, where the mutant had managed to scratch him. "It's not a deep wound, but I'll need to clean it thoroughly. We don't know what kind of toxins these things carry."

Klaus, still trembling, pointed towards the mutant's lifeless body. "What... what was that thing? It wasn't human."

Stefan shook his head grimly. "The GCE did more than just poison the land. It warped the very creatures that lived on it."

They continued their mission, but the encounter had changed the atmosphere. Every shadow seemed to hold a potential threat, every rustle of leaves made them jump. They reached the power substation, but the initial excitement was gone, replaced by a gnawing unease.

They managed to salvage some scrap metal and wiring, but their hearts weren't in it. The memory of the mutant's grotesque features haunted them. As the sun began to dip below the horizon, casting long, eerie shadows across the Tiergarten, they decided to return to the Citadel.

The journey back was uneventful, but the silence was heavy with unspoken fears. They reached the Citadel gates just as darkness fell, relieved to be back within the relative safety of its walls.

Marcus met them at the gate, his face etched with concern. "What happened? You're late."

Stefan recounted their encounter with the mutant, describing its horrifying appearance and its relentless aggression. Marcus listened intently, his expression growing increasingly grim.

"So, the stories are true," Marcus said, his voice low. "The GCE didn't just contaminate the land. It twisted and mutated the wildlife. This changes everything."

He looked out at the desolate landscape surrounding the Citadel, a vast wasteland teeming with unknown dangers. He knew that the task of reclaiming the surface was going to be far more difficult than he had imagined.

"We need to understand these mutants," Marcus said, turning to Sarah, who had joined them at the gate. "We need to learn their weaknesses, their habits, their origins. This is no longer just about rebuilding society. It's about surviving in a world that has been fundamentally changed."

He knew that the Citadel, and the hope it represented, was now facing a new and terrifying threat. The mutants of the Tiergarten were a stark reminder of the GCE's devastating legacy, a testament to the fact that the world they were trying to rebuild was a world forever scarred. And he feared, deeply, that this was only the beginning of the horrors they would face in their struggle for survival. The Obsidian Eye had reshaped the world, and the creatures of that world were a reflection of its malevolent influence. The future, once a distant glimmer of hope, now seemed shrouded in a chilling, uncertain darkness.