Need bad guy plot for story, help?

Maube the bad guy could have poisoned her mom (or something like that) and he poisons the land so that he'll be able to fake being a hero because he'll have the antidote and use that to make himself the king. Then when he hears about Kathryna going to the human realm he sends guards to catch her or goes after her himself to stop her from getting an antidote. Hope this helps! :)