Easily level up Master Form by going to the corridors outside Ansem's Lab. Leave Ansem's Lab and go to the first main room. Three Crimson Jazz enemies should appear. Change to the Master Form, beat the enemies, and collect the orbs they drop and keep moving to the other enemies. It's possible to kill them all within the same change. When you Drive Gauge depletes, go to Olympus for a recharge. You can find seven Crimson Jazz enemies for a total of 70 to 80 XP each time.