You want to do the Catfish level. It's advised you have a decent amount of skill points into Magic and a lot of points into Agility (Magic for splash magic spamming purposes and Agility for dodging) When Catfish appears, spam splash magic. If you have a character with decent boss slaying then you should earn XP quickly. You CAN remove the hairball, but to the risk you do high damage. Do NOT attack it when the King launches the cannonball and it's stunned; otherwise it'll take a massive amount of damage to Catfish. When the Catfish starts attacking you with its paw, block it with your shield. Keep repeating this, and you should get lots and lots of XP.