When you need to fight against the Giant Trol a player must run around him and distract him. Quikly after the Giant Trol spits fire you can attack him with your long range weapon, and when your Mana Bar is full, you can use your ultimate attack by pressing the Black Button. This is easier if you play with more then 2 players.

Note: It might not work, but thats how i defeated the Trol.

To easily level up with the Wizard, go to the Imperial Palace level. Towards the end is a room with endless red beasts, and you must find the Magic Key in it. These beasts are extremely easy to kill. Go in to the center of the room and repeatedly use the Path Of Sky attack by pressing A. The beasts will keep appearing, and you will continue to gain experience. This works best with a controller with a auto-fire feature.