...upgrade your fighter class to "Generic Light Warrior" and use your "Sword of Light" of course. Approach the Shadow and you MUST perform a 99 hit Super Combo finish, which should give you 30,000 points for using level 3 and a 30,000 point Perfect bonus. If you did not do 39,999 addition points' worth of hits landed and the combined score is not 99,999 or higher you did it wrong and need to start over.
Now that we can finally stop making so many Pokemon references (this is a Mario cheat after all) start speculating where you should search next. Perhaps we should investigate the plague that says "L IS REAL"? Approach the plague and...