Pax was as normal as normal could get.
He was a normal earth pony, with uninteresting cutie mark, and uninteresting future. Pax refused to accept his role in life, he wanted to be a great hero, save Equestria! Just like the six elements of harmony!
However during his attempts he found an old a sealed away evil. Without knowing the danger, Pax struck a deal with the creature and gained the powers he needed to become a hero!
Unknown to him, he had unleashed an unrelenting evil upon the lands. After being confronted and exposed, Pax was locked away as the elements tried to seal the creature away once again.
Wanting to make up for his mistakes, Pax sacrifices himself, bonding with the creature, trapping it inside himself and then seals them both away.
Now he's trapped for eternity, leaving him to deal with his shame and guilt...