Scaling options for muscle-ups: Perform the M/U to the best of your ability. If you are proficient with 2-4 reps, then perform 2-4 reps. DO NOT get stuck on the exercise. Practice, attempt and move on. If you can perform a “jumping” m/u, then I suggest doing those. Bar muscle-ups are also an option. If you cannot perform the movement at all, then perform 6 chest-to-bar pull ups and 6 dips in lieu of the 6 muscle ups.