Celestia paced about the throne room, thinking about what to do about the multitudes of disappearances near the Everfree Forest, far to the south. She could not cut it down, as many times as she'd tried, and she could not keep her subjects away from it, for there are always adventurers, willing to risk everything for a good time and some treasure. But if she did nothing, the brutal murders would only continue. The incidents started a month ago, when she sent her last logging expedition into the forest, only to have one worker out of 213 return half-dead, and find the rest of them dead, torn to shreds by something bigger than a manticore, and more vicious than a pack of timber wolves. It became official when she sent a contingent of guards to deal with it, but none returned. Instead, they all turned up in the same condition as the expedition, but with their heads removed. Now, the murderer is slowly expanding its reach outside the forest, targeting everypony from explorers to simple passerby to patrolling guards, all with the same result: heads cut off, violently. She needed to find the source of these atrocities, but that meant entering the forest. Since it seemed to attack the weak, she assumed it to be an easy kill for her, so she wrote a quick letter to her sister, Luna:
"Dear Luna,
I am going to destroy whatever's killing our subjects in the Everfree. I will return shortly.
Sincerely, Celestia."
Once she'd left it where Luna would find it, Celestia flew off toward the Everfree forest, eager to meet whatever was causing her this grief.
Later, at the Everfree Forest
Celestia landed in a small clearing she made initially for her deforesting expedition, and looked around, though what she thought to find was unknown. The machinery used by the deforesting team was all still lying around, and the blood from the initial attack had all washed away. Indeed, it looked like nopony even died here, or had ever been here at all, save for the out-of-place machinery. As she searched the clearing, though, Celestia heard a rustling in the shrubbery, but paid it no mind.
Little did she realize, some predators and their master were watching nearby... and they were hungry.
A strange creature watched from the shadows, his spines looking like trees, and his teeth white and sharp as razors, and followed by several timber wolves, all hungry for the new prey's blood. However, the strange beast held them back with but a glance. This new prey was dangerous, it knew, and he would not sacrifice his packmates so easily, if just for this mere pony. Instead, the great, reptilian beast itself rose from the bush, and and approached the newcomer, startling her. Though the shock on the new prey's face was genuine indeed, she had intruded on his territory, and now would pay the price all those before her have paid. The beast let out a colossal, earth-shaking roar as he faced his opponent, who was now taking a combat stance of her own, despite of her comparatively small size. Odd prey, indeed...
Celestia first saw the behemoth rise, and watched in shock as it approached her, letting out a horrible, demonic growl as it strode, the beast's impressive muscles flexing and shifting as it moved. She took a defensive stance as she studied the odd creature, which didn't fit the description of any creature known to her or ponykind in general. For starters, it was slightly bigger than a manticore, but it was reptilian, with impossibly-sized muscles all over its scaly body, giant, barbed spikes running along its back haphazardly, and a long, box-like head, with two red eyes and a single, horrific row of long, sharp teeth, which it bared with a look of utmost ferocity, and likely desired nothing more than to sink those teeth into her. When Celestia had finished studying the immense creature, which she was now sure was the culprit for all the murderers, it finally let out the biggest, most guttural roar she'd ever heard in a very long time, and pounced, quickly covering the distance between them in a single bound. Clearly, those muscles weren't just for show.
As the monster landed, Celestia dodged a swipe of the creature's claws, and then cast a great fireball spell at it, hoping to incinerate the beast before more lives could be claimed by it. The creature, however, put it's forelegs up in a defensive stance, blocking the fireball. Then it turned and swatted Celestia aside with a swing of its spiky tail, causing her to fly through a few trees before scraping across the ground for a good few seconds. Whatever this thing was, it clearly wasn't as stupid as it first seemed. As Celestia got up, the beast was already crashing toward her, teeth bared and ready to chomp down on her. But Celestia had other plans. Charging another giant ball of magic, she released it just as the monster leaped into the air, causing it to fly backwards as the spell made contact and exploded, giving her time to get up and fly out of reach.
Celestia couldn't fight this thing, whatever it was, but she knew six ponies that could. And so, Celestia then flew away to Ponyville to find said ponies, and proceeded to leave an angry, grumbling monster behind.
The great, reptilian behemoth watched in anger as his prey up and flew off, having been the first in a long time to have escaped his wrath. But the beast could find more. His pack never starved, for there were always fools who would trespass on his land, and they would always be easier to kill than the one that got away; they always were. As he returned to his cave, the beast then began to change, becoming smaller, but still heavily-muscled, standing on two legs, and his head became taller and flatter. putting on his cloth garbs, the odd creature then picked up his staff, then began the hunt for different prey to feed his creatures of the forest, presumably prey that wouldn't fly away or throw giant fireballs at him.