Tugging from the shoelaces. Biggest deficit I've ever done on sumo. Hip mobility has come a long way despite zero passive stretching. If you want changes in mobility, you have to load the position and work on strength at end range.
I'm going to play around with not doing any barbell squatting for a while. Instead I'll do all yoke squats from different heights and see what happens. Partial range work like this is the best way to address sticking points on the lifts. Talking about how low you squat but then being stuck at the same weight for three years makes you a dumbass (referring to myself obviously).