Stymnus

This happened to me also but in the abortion clinic boss fight (Giant Nazi Zombie Fetus)

Maybe this has been covered, but Butters' Professor Chaos attack is bugged versus the Unplanned Parenthood main boss. If used, there is no further visual representation of what you do (not even getting to select the wheel) though you can in theory feel your way through the combat. Just can't see your guys or what they're doing. You still get menus, but it becomes difficult to know what's going on.