Once you've become a grand champion, the lady managing the arena will offer you random (but tough) fights each game week. If you want some easy gains, ask for a fight against three minotaurs.

Once the announcer says, "Lower the gates", remain in the steps to the entrance hall. Shoot a few arrows or spells at the targets, and all you have to do is stay close enough to them to attack. Occasionally one minotaur may get through but you can handle one fairly tolerably by then.