Poison Ivy- Batman & Robin
Poison Ivy isn't inherently evil, which kind of makes her role a bit more understandable. She merely sees the evil in humankind and chooses to address it with "unorthodox" tactics, and by unorthodox we mean murder. She is a master manipulator who merely wants to save the Earth, causing her character to both to be relatable and fearsome at the same time!
Kathryn Merteuil- Cruel Intentions
Although Sarah Michelle Gellar played the hero Buffy in Buffy the Vampire Slayer, she performs some seriously diabolical roles in some of her earlier movies. In fact, her acting in Cruel Intentions is some of the most dangerous and manipulative acting we've seen to date. Not to mention her role in Dangerous Liaisons, which was just as scarily terrible, yet entrancing.