Unlimited Training At The Sol Sanctum
When you are at the Sol Sanctum, you will encounter monster quite frequently until you are level 5. When you are past level 5 you don't encounter any more monsters there. By doing the following you can keep training there even when you are past level 5. Make sure Jenna is level 1 then go into a battle and let her die. DO NOT REVIVE HER. Isaac and Garet can keep leveling now.
More tricks, tips and cheats for this game are right here - Golden Sun: The Lost Age cheats
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