Lots of Mugwort Herbs:
After you meet Koris for the first time in the Beetle forest, select "Attacks and Defense" and start training. He will give you a Mugwort herb. Now during the battle, on the first, second, or third turn ignore what Koris tells you to do and select a different command (except item) and he will tell you that you must obey. The fight will end and you will have an extra Mugwort Herb! You can repeat this until you have as many herbs as you like. Unfortunately, the item maximum is 20.