Anorexia Nervosa!
 
Best Friend of: An undead sheep and an undead wolf
 
Backstory: She was just jealous! Having been born an earth pony with a Unicorn and Pegasus for parents, the young foal who’s name was not originally named Anorexia (Her original name is unknown) was extremely jealous of those who were naturally born with greater gifts than her.
 
She applied for Celestia’s School of Magic, and was brought before Celestia after months of re-applying, to be asked why she was so adamant about enrolling. She said she wanted to study magic and write essays on how it works so that Earth Ponies and Pegasi could understand the magical workings of Unicorns.
 
She was accepted, and wrote several essays over the years, and at one point she made a huge discovery: The Harmony Spark.
 
The ‘Spark was the foundation of pony magic, found within ALL ponies, from Earth Pony to Alicorn. Unicorns could channel it through horns, and Pegasi through wings (Though it’s very hard. See: Sonic Rainbooms and lightning/rainbow trails during flight.), but Earth Ponies couldn’t channel it at all.
 
She couldn’t accept this.
 
She decided to attempt to extract her own Spark to study it, and in the process wound up breaking it. She went ABSOLUTELY crazy. Like 100% batty. In her insanity, she dug up the grave of a unicorn, and used their horn to channel her own Harmony Spark, and in doing so cast her first spell, a spell that prevented her body from needing food or sleep. In casting that spell, she figured it out, and started using magic regularly.
 
Celestia found out what she did and she was locked up in Tartarus. She escaped, and not just that, she erased the memory of her existence from the school, and from the princesses, and went off to practice her magic elsewhere.
 
She painted a new cutie mark on, which is the skull of the unicorn she dug up, which she calls “Smiles” and talks to regularly (Both her cutie mark and the actual skull). She knows how to do magic as an Earth Pony but can’t figure out how to put it into words to teach others because she’s nutty.
 
Her personality can best be described as: