I adopt this character from famous artist Sapphirus

Lord Dexerus is an evil spirit that most poeple know him through anceint legend. Lord Dexerus almost try to rule the wolrd with his dark magic, but was stop by his elder sister Tealos the guardian of light. When TEalos use her magic to seald her brother away into another dimension, Dexerus use his dark magic to curse his elder sister, transforming her into a fox creature, and erase most of her memories, then place her inside a solar stone. Trap inside at an alternate Dimension, Dexerus use his powers to make an mega stone that corrupt certain pokemon and take control of their mind, and use them to helpp him find the solar stone to set him free. But since he couldn't do it on his own, he found a student name Rebecca, who he promise her power, if she help him the right pokemon to use his dark stone. If Dexerus ever break free from his prison, he will be impossible to stop. He already know that his sister have an allie to try to stop him. Dexerus will have no problem of stopping them on his own.