To earn lots of experience make a backup of your original play disk.
Now boot and insert the disk that contains your characters. Save
them onto your second backup by going to the inn. Buy three tickets (green, yellow, red or black) and try to win in all three arenas.
Remember to save after each victory. Once you have a victory in
each arena, go to the castle where the bishop is held captive.
Before entering flick the write protect tab to protect your disk.
Then enter and free the bishop with the correct key. He will give you experience if you have won three fights of the same color. Exit and go to town. Open write protect tab and save at the inn. You
can repeat as often as you like.