The black coated pegasus trotted up and knealed before his master, "The job is done, as you requested, sir." There was a loud rumbling, as the entire cavern shook. A couple stalagmites fell from the roof, none hitting the black coated pegasus. A larger than average unicorn came from the depths. Completely black, like the shadows. It trotted up to the pegasus, and tilted its head as if looking at him.
The thing, the large unicorn's color began spreading from its so-called-excuse for a cutie mark. It was still black, just a brighter shade, like a pencil led grey. It's mane was clear white, such that it was supposed to represent heaven. The so-called-excuse for a cutie mark had nothing wrong with its features, it's just that, is it supposed to be cute? It was a flaming skull with red eyes, and blood dripping from the jaw. The color spread further, and the unicorns hooves were also matted with blood, all kinds. The eyes opened, a bright red filliment, like the devil had its entire eyehole painted red. One of the ears were missing, and there was a hole in its horn. "Good," it said in a deep, dark voice.
The pegasus lay out the contents in its sack across the floor. The maroon blood of a pony, the silver blood of a unicorn, the bronze blood of a pegasus, and hardest and to get, and scariest of all, the gold blood of a alicorn, all concealed in 4 vials. "Yessss... Good job, now we can commence phase two..." it rumbled.
It walked up to a small bump in the ground, and spilled the four vials' contents all over the bump. Nothing happened for a moment. As it was just about to speak, a large rumbling, much larger than his intial one, occured. The stone where the bump was cracked, and an object shot up out of it at gut-splattering speed. A golden fountain appeared out of it, with four seperate oblong sections arranged in a circle around a single pillar with four nozzles pointing at each section. Seconds later, the nozzles began to hose out four different colors of liquid. Maroon, silver, bronze, and gold, the blood of the pony world. After the four sections were filled, they started to glow a malelovent greenish orange, and the nozzels each exploded with black liquid. One drop touched the large grey unicorn, and the holes in it's bodies, and the ear reappeared and healed, and he became normal size. "I have no use of you anymore," the unicorn said the the pegasus, and the unicorn stamped his hoof on the ground. A hole appeard beneath the pegasus, and it fell down the hole, and the hole closed before the pegasus could escape.
"Yes, finally, now I can comeplete my mission," the unicorn trotted this way and that, until it reached the entrance of the cave, and exited. The newly raised sun's rays cast across his eyes, which he squinted. His pupils adjusted, and he trotted down the hill, and became Celestia once he reached the foot of it.
"Finally, infernal ponies, it is time, to pay!"