Before starting any Dojo complete 'Location 8 - Ninjago City North' to unlock the Master of Endurance Ancient Scroll (Invincibility). Replay the stage again in freeplay and collect the Master of Fortune Ancient Scroll (2x Stud Multiplier):
Activate both of these Ancient Scrolls and defeat the 3 waves of enemies followed by the Dojo Leader. Aim for a 100 hit combo to get the High Score and unlock the Gold Medal for this stage (90,000 Studs).