Ever since the three tribes first met each other there have been stories of a fourth tribe with traits of all three. Some sources call this fourth tribe pegacorns, or unisi, but since they are rumored to have the enhanced strength of earth ponies in addition to wings and a horn, we will be using the name alicorns. All stories about alicorns include their incredible magical abilities. Some stories mention the same alicorn appearing at different times sometimes hundreds or even thousands of years apart, suggesting that alicorns are immortal, or at least very long lived. Some have even suggested that the exact same alicorns appear in all the alicorn stories. The most recent alicorn story is the story of Nightmare Moon.
Hundreds of years ago the unicorns in charge of the sun and the moon would often report the feeling of two powerful being helping them. One helping with the sun, the other helping with the moon. However this changed one day when the moon refused to set and the sun refused to rise. The unicorns could feel the same being that once helped them with the moon now preventing it from setting. Every unicorn from across the land was brought together to try to raise the sun. They poured all their magic into raising the sun until they all collapsed from exhaustion but still it did not rise.
The extended night did not go unnoticed but the pegasi and earth ponies. Back then the three tribes were still wary of each other so the earth ponies and pegasi mobilized their armies and sent them to Canterlot. When the unicorns saw this they immediately mobilized their army to their defence despite of their exhaustion. However before it came to a battle a dark alicorn mare appeared. Her coat was the deepest black, her mane looked like the night sky, and her cutie mark was a crescent moon. Her exact words are not remembered but she called herself Nightmare Moon and claimed "The night will last forever!" Upon hearing that claim all three armies attacked her. After a few hours it was clear the armies of the three tribes would lose and when all hope seemed lost a second alicorn mare appeared.
The second alicorn had a pure white coat, a blue, green, purple, and pink mane, and a cutie mark of the sun. Again her exact words are not remembered but she referred to Nightmare Moon as her little sister and told her to fight the corruption that was in control of her. The younger alicorn attacked the older. The older alicorn teleported them both to the center of the Everfree Forest. Flashes of light continued over the Everfree Forest for many hours ending in a brilliant flash of rainbow colored light and the face of an alicorn appearing on the moon. By then it was already time to raise the sun for the next day. The unicorns easily raised the sun but never again felt any powerful beings helping them nor did either alicorn ever return.
Though it is unlikely any of this legend is true there is one more part of this story. These events are said to take place in 537 E.E. The myth continues to say that Nightmare Moon is the one sealed on the moon and on the summer solicist one thousand years after the battle the stars will aid in her escape.
"But, thats in a week!"