I recently was made aware of Etsy artist deliciousness' amasing custom illustrated portraits, perfect for invitations or Save-the-date cards. You and your groom can choose your favorite mythical creature, send a picture of yourselves and recieve this bright, cartoony and sweet portrait of you riding the beast :-) For a medieval wedding a dragon/unicorn or the likes would do perfectly. Especially if you are having a more modern version of the theme wedding. One where you would like medieval to play a minor role in the details.
A Danish bride and groom ordered this picture from the shop, a sealion/dragon creature: