Here’s Charcoal “Yzal” Blast !
 
She’s a miner who was caught in a magic explosion at work. The explosion blasted her out of the mine, she survived but the right side of her body and most of her back were burned in the process. She was given magical prosthetics but can’t keep both her leg and arm if she wants to use her magic, which she doesn’t mind since an arm is pretty useless when you can make things levitate.
 
Her nickname, Yzal, came from her coworkers. As the only unicorn working in this specific mine she was seen as very lazy by the pegasi and earth ponies there, which she actually is. They didn’t want to say it right to her face so they just put it backwards thinking it was clever and hoped she didn’t notice. She never did, because she’s kind of a moron, but as she was a pretty great gal to work with the nickname lost its original meaning pretty quickly.