Hi! Once you find all the moons and open the Lunar Amulet, you'll find a new file inside the directory. Copy that and overwrite the original one inside the game directory and you'll find the Full Moon item inside your inventory. Then you can give that item to Master Mathias... sooner or later. You'll have to complete the Stellar Amulet first! So, if you haven't done it yet, you need to defeat the Mastermind first, and then talk to Maverick. Anyway you have to collect all the stars to proceed : )