The way I understood it is that if you have in your inventory the following items:
Four-leaf Mandragora Bud
Lucky Egg
Wild Rabbit Tail
...as well as having a Millionaire Desk set up in your Mog House.
Then you need to face the enemy you are engaged to towards the south east. It also needs to be New Moon.
It also needs to be a Full Moon in real life. You need to spin around in your chair 3 times. Then touch your left index finger to your nose and say: Abracadabra.