False Grip Pull-Up

Grip the bar with your wrist rolled forward so the bar sits in your palm below your fingers rather than your thumb wrapping underneath; your wrist bends back over the top of the bar instead of hanging straight down from it. Pull up as you would for a normal pull-up, keeping that same wrist position through the whole rep rather than letting your grip roll back to normal partway up. It's an uncomfortable position at first and puts real strain on your wrists and forearms, since they're holding your bodyweight from an angle they're not used to. This grip is what a muscle-up transition needs, so practicing pull-ups this way builds the wrist and forearm strength for that movement without adding the muscle-up's timing on top.