As far as antimatter goes, considering how hard it was to partially transfigure, I Imagine it would be impossible to craft something foreign to most people's understanding without a lot of practice, and anyone who tried to practice would explode the first time they succeeded.

I can't recall If there's a canon limitation on Imperius curses, but I imagine they are strictly limited in MORverse simply because if they weren't the entire wizarding world would constantly be suffering from constant control of everyone by everyone.