Two stallions stared across the river they stood on the bank of, each one bearing a face of confusion. One, a brown pegasus pony with a black mane and tail and a farming scythe cutie mark turned to his companion, nervously chewing on the twig he had in his mouth.
"What in Sam Hay do you think it is?" The other, a pastel blue earth pony with an indigo mane, his muzzle silvered with age, uneasily shrugged.
"I...don't know? When did...THIS even show up, Hayseed?" The pegasus shook his head and flattened his ears, looking back across the river towards the monstrous corpse.
A buffalo- but only in the faintest sense. It's horns had twisted wildly and grown so long that they had begun to tear into the poor beast's neck, and long fangs had ripped from its mouth, mangling its muzzle. One leg had lost all its fur, another had shortened. Its tail had broken several times, each time apparently trying to heal into an entirely different shape, and several patches of the mangled mammal's hide had fallen away to reveal patchwork scales that it had scratched at until they broken. It was a twisted amalgamation of mutations- and burns that could only be caused by magic surrounded its eyes and nostrils. The carcass's lower half was partially submerged in the water, and even as the two ponies watched, another clump of brownish red fur detached and drifted away.
"Sometime since last night, Whistle...And that ain't even all." Hayseed turned to one of the bushes that lined the riverbank and pulled a branch off, then tossed it into the river. The instant that it touched the surface of the water, it seemed to ignite, burning up in a flash of arcane fire. The earth pony opened his mouth, only for the pegasus pony to hold up a hoof, indicating that he wait, then pointed as the fire seemed to peter out, leaving behind a neon pink and green-spotted snake with five eyes, which then hissed and crossed the river to hide in the rushes on the side opposite to the two stallions. Whistle's eyes widened, and he flattened his ears as he looked at Hayseed.
"The river's contaminated, Whistle...anythin' live that touches it gets...strange."
"Impossible- this river isn't magic or anything, there has to be some sort of explanation. This stream comes from right by Ponyville, maybe somebody dumped somethin' they wasn't supposed to." Hayseed winced and backed up a step.
"Well whatever the explanation...any livin' thing that touches that water, something unnatural happens to it. Some items too- we can't even pump water to irrigate the crops! Some of the pipes broke apart and started singin' opera...then started arguing while singing about which one could sing the best."
Whistle rubbed the back of his head nervously, glancing once more across the river towards the tortured corpse. Hayseed watched him nervously, then blinked and looked over his shoulder as a unicorn colt, who couldn't be older than twelve, galloped up, shouting Whistle's name. Whistle turned to look at the colt as the young thing skidded to a halt in front of them, wheezing and slick with sweat, then looked up.
"Mister Whistle Wit! Th-the lady of the house, sh-she was in- I-I mean she's-" Whistle put a hoof on the colt's shoulder to try and calm him apprehensively.
"Calm down Nettle- what's up with Belle?" The colt took a big gulp of air, then whimpered softly.
"She was- she went down to the bank for her mornin' bath, and-" Whistle's eyes widened and he immediately twisted to run downstream, hooves beating against the ground as fast as he could push himself. The instant his wife's screams hit his ears, he dove through the branches to find a petite white pegasus mare with a wine-red mane thrashing in the shallows of the river, strange looking magic clinging to her fur as she seized and kicked wildly- her hooves were cracking and splitting, her wings quickly becoming bare of feathers as strange looking bat-like fingers stretched out from the spasming muscles instead. Whistle dashed for her, preparing to jump next to her side, only to be tackled before he could reach her. Hayseed shook his head desperately, struggling to restrain his boss.
"Sir, no! Anything the water touches!"
"Damn it let me go that's my wife-!" The poor mare's screaming rang in his ears as he thrashed- so much so that he didn't hear the splashing until after his wife's sobs stopped, and the backlash of a magic surge seared his pelt. White and black spots filled his vision and static rushed in his ears even as the heat faded, and he felt Hayseed's weight lift off of him, then felt the impact as the other stallion promptly fell to the ground not even a few inches from him. It took several moments for his hearing to return, and it returned to eerie silence except for the tiny sobs coming from his wife.