The antagonist of my first novel is much different, in my prequel. She needs to grow into a sociopath, by the end of this book. I needed to create characters and events to transform her personality.
In mythology, Medea shifts personality after Jason abandons her. Medea begins the tale as a super-powered heroine who helps Jason, but in one version of the tale—she kills their children, after the abandonment. I probably should consider paralleling Medea, in some way. Love rejected can cause significant emotional problems and is something I should consider.