Miruda the Radioactive Queen

Queen Miruda is an alicorn that had been born in an inhospitable land full of harmful, ionizing radiation. Her mane and tail have a very similar composition to toxic waste. Miruda's crown is actually part of her body. Her body absorbs and emits ionizing radiation such as alpha, beta, and gamma radiation; since her diet mostly consists of organic (and sometimes inorganic) material withh highly radioactive properties. Her body is comprised of the typical organic material in a pony, but 40% of that is flexible, low-density polyethylene (plastic). Miruda sometimes can't fly correctly due to occasional muscle spasms in her wings that occur at seemingly random intervals. The crooked shape of her horn was the result of genetic mutation.
Miruda's magic has to do with harmful radioactivity, altering the stability of certain atoms' isotopes, and nuclear fission.

Miruda made her home in an abandoned nuclear power plant on a remote island called Shadow Brook, feeding off of the radioactive particles emanating from a reactor's exposed core. This land is home for many hideously mutated ponies and ponylike creatures whom Miruda rules over. The murky gray clouds that hover lifelessly in the sky and block out a majority of the sunlight gave the land the name of "Shadow Brook". Due to an accident that happened on that island many years ago, no other pony had set hoof on the island ever again; this made Shadow Brook seem like an Alcatraz for the unlucky mutants that never sprout wings.
The cycle of absorption/emission of the land's ionizing radiation is controlled by Queen Miruda. Miruda knows not to leave to any other land where normal healthy ponies dwell due to a bad past experience that nearly wiped out a small town's population.