Sombra.

King Sombra has a horn on his forehead that contains magic, black hair, a spiky tail, and fair skin. Unlike a normal unicorn's horn, which matches the color of a normal one and is straight and ringed with several rings, Sombra's horn is curved, smooth, and sharp at the tip, and its color ranges from dark gray to red. The King has sharp teeth with two visible fangs, unlike other ponies, and red pupils. Green and purple mist emerges from the whites of his eyes, which disappears when he is attacked. He wears silver greaves and a gorget, a horned crown, and a red royal robe that covers his back and rump. When he was turned into a shadow in a memory, only his head remains, and when he returns as a shapeless black cloud, only his eyes are visible at first.
Tyrannical and power-hungry.
Arrogant and self-confident.
Revengeful.