Hydia is the main antagonist of My Little Pony: The Movie - which was based on the Generation 1 franchise, which was very different from the current version of the show and more akin to what people associate Care Bears and other "kid-friendly" franchises as being.
Despite this Hydia was depicted as a geniunely malicious villain who had a stereotypical "wicked" demeneor and sought to utterly ruin the world around herself as well as abuse everything for no reason other than she could, she was also apparently part of a long legacy of witches and warlocks who glorified being wicked for no reason other than they could.
Hydia was especially abusive towards her two daughters Reeka & Draggle, to the point of punishing them for calling her "mommy" - a short-tempered crone and all-around nasty woman she lived within a volcano and cast many evil spells in her eternal crusade against all things "nice".
Ultimately Hydia's plans would see her raise the abomination known as the Smooze, a gargantuan slime-monster that was almost unstoppable and very nearly destroyed all of Ponyville - however in the end Hydia was defeated and both she and her daughters were cast back into the volcano but would return in "The End of Flutter Valley".
The End of Flutter ValleyEdit
Sometime after the events of the movie, Hydia would return and ally with a group of giant bees to exact revenge on the ponies for her previous defeat - causing great chaos in what would be a 10-part episode of the My Little Pony TV series.