Go to Gittingham Palace in the ruins of the Gitt Empire. After entering, move counterclockwise around the first floor until you find a staircase. Climb staircase and go to the hole in the floor. Directly next to the hole is a bookcase, with a book that is actually an ancient sage sealed into it. The Supreme Sage tells you that to become a sage you must defeat five great trolls with Frizz. To do this easily, find out how many attack turns it requires to kill the great troll. Then, attack all out for a number of turns that is one less than what is needed to defeat it. Next, let the mage finish the battle with Frizz.