Not sure how busty to make Mastermind here. I thought I'd go with Grace sized, but I could go all the way up to Annie's size. But I didn't know if that would be too distracting. It's more meant to be something silly, not overshadow the rest.
I like the differences here between Mastermind and Mira here from the real world. There, Mira is the taller, bustier one. Here, Mira is shorter and thin- and Mastermind imagines herself bustier.