Backstory-

This interesting mare right here is Xeno (pronounced Z-No) she was a regular Earth pony teacher of Canterlot before she read a book about an Earth pony who became a unicorn. She had always been looked down upon by her fellow teachers who were mostly unicorns, save for a couple pegasi. She wanted the respect of her peers even though she liked her job teaching the youngest foals and fillies about the nature that surrounded them. She decided however that it would be beneficial to her life if she could change her race.

Naively she chased a rumor and at a dark chasm she met a nightmare willing to give her what she desired but at a cost. He needed help getting out of his prison as he was too weak to do so himself. He asked for her to bring him a foal and filly of each race and he would give her the magic he desired.

Xeno was a very foolish mare and against her better judgement she did as he asked, leading the six young ponies away from their school on a 'feildtrip'. She brought them to the nightmare who dragged them down the chasm walls into the abyss below. He broke free and she was ready to receive her reward.

However as one should never make deals with a nightmare her wish was not granted as she did not bring him two young alicorns. It hadn't even crossed her mind as an option and for her neglect her wish was mutated as well as her body. She received the magic she was after but her desire to be be accepted would never come to pass as her new appearance would ward off others for years to come.

She tried to run from what she had done, and what she had become, but she grew tired after a while and she now stays in the Everfree in a cave she made from the magic that cost her everything.

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Personality-

Despite her history she is a very friendly mare if greeted with kindness. Her history has left her rather bitter though and if a pony so much as spot her and give her an odd look she'll retreat and not come from her cave for days. She's made friends with only one mare so far who, similarly, discovered the same magic and with this friend she's begun to accept herself more, but she has a way to go before she's ready to leave the forest.

Her greatest fear is being arrested for her crime of leading the six fillies to their death. She wishes nothing more than to take back what she did. She's becoming more interested in learning about the power of nightmares, even if she refuses to use her own for anything other than good or neutral purposes. She's learned that discolored hooves are a side effect of an Earth pony using unicorn magic and that it travels through their hooves instead of a horn. She's working on finding a way to change this though as she's motivated by her friends insecurity about her own hooves.

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(So I've decided that I officially don't have a problem making OC's that don't fit in the MLP universe. Why? Because there is no law that says I have to, and I want to let my creativity be free from constrictions created by other people. I'm sure that'll anger people, but I'm not hurting anyone so I guess that's their issue and not mine.)