Mystique Incarcerated

Part of the job description for being a super-villain is that you're going to get caught.  And that means they have to keep you confined.  And someone like Mystique isn't going to be held by just cement and bars.  So they have a special room for her: Brass coated titanium bar restraints with a mesh interior that contracts if she turns into a little girl and tries to slip out; visual and audio input devices that keep her in a semi-conscious docile state; and sophisticated motion sensors that monitor her constantly.

And you don't want to know how she uses the bathroom.  But that's the price for being a bad girl.