There is a different way to do 20 rep squats that I haven't seen mentioned here yet. That is the rest/pause squat. Basically, you take your 10RM squat weight and complete your 10 reps, rack the bar, take a bunch of lung-filling breaths to recover a little (not too much), then shoulder the weight again and do as many reps as you can. Repeat this process until you've completed all 20 reps. This allows you to use a higher percentage of your 1RM for the exercise.
I've even seen guys use 20 heavy singles before, that would be brutal for sure.
Has anybody tried these?