“The destroyer of worlds, the anarchist, the being with absolute power that could rival that of the omnicorns. While she is known under many names, Mtyholi, Death-bringer, Savylon, to name a few, the most common name uttered was Erebus. She reigned as Queen of the Monsters in Equestria before its proper foundation. Of course, she was far older than any record of pony history. Older than the planet itself. She watched the world form under her paws, and from the beginning she had sought to destroy it.
 
Erebus was a shapeshifter and she was bound by no rules set in place by the omnicorns at the “creation” of existence. Erebus was the bane of immortal and mortal life, as she interfered freely with their plans, and they were almost powerless against her will. It was all they could do to prevent her from just snapping her fingers and transforming the world they had created into an apple, which she could simply devour. Nobody understood this being beyond what frightened them, and no one could ever blame them for that. Erebus ruined countless lives by unleashing ungodly monstrosities unto the budding pony society, and she is the most likely suspect of the destruction of Tempest Mountain.
 
Upon her forehead was a mysterious third eye which always remained open, allowing her a certain omnipresence over the world. She could see truths that would drive the average pony into madness, but those particular truths remain unknown to us all. Perhaps this is for the best for those that dabble in such magic are lost*.
 
No one knows for sure what happened to Erebus. All that we can say for sure is that she perished the exact moment Tempest Mountain erupted into nothingless, leaving Princess Luna and Celestia as the sole alicorns of the world.
 
*Loss refers to the disease known as Crystal Blight. Unicorns are the most susceptible to the disease, which fogs the mind withhallucinations and horrendous nightmares, before the body is entirely consumed by dark crystals resembling those of King Sombra. See glossary for more details, disclaimers and warnings.”
 
-Excerpt from Janus’ novel Pre-history: An Analysis of the Equestrian World vol. 2