You'd have to cure him of being a werewolf first if you have a sim whom does alchemy (need high level) you can make Potent cure elixir with alchemy station then make a fairy potion.
You need bottled blessing of the fae you can buy it at the alchemy shop sometimes it's not there right away you have to keep checking for it or if you have a sim that has a level 10 alchemy skill if they have the ingredients they can make a bottled blessing of the fae Ingredients- Red Toadstool, Sunstone, Fairy Damsel Fish -Become a Fairy
OR if one of your friends has those bottles they can send it to you via the free in game gifting all they have to do is if they have that bottle in their sim inventory click send as gift to friend then the friends list should open then pick you and send it then you get it from the mail box accept gift from friend
