Charles Xavier's twin sister, thrown out of the world and given a rubbish tip to rule, with all of his power and none of his patience.
Cassandra Nova is the sociopathic British twin sister of Charles Xavier. She was pruned by the Time Variance Authority and rules the Void with a gang of supervillains, and she is an Omega level mutant: telepathy through touch, telekinesis, phasing and teleportation.
Emma Corrin plays her calm, curious and completely uninterested in being frightening, which is why she is. The film’s best scene is a conversation, not a fight.
Minor spoiler
Her gang brings her the captured Deadpool, Wolverine and Human Torch. She kills the Human Torch and the other two escape and lead the resistance back to her. They subdue her with Juggernaut’s helmet, and when Pyro shoots her, Wolverine takes the helmet off so she can heal, because he thinks that is what Xavier would have wanted. She lets them leave, then follows, learns about Paradox’s Time Ripper, kills Pyro, and tries to use the device to unmake everything. Deadpool and Wolverine overload it and she is atomised.