While you have more freedom with this dress code, there are still clear rules for what not to wear to a black tie optional wedding
Easy enough: Find a bright blue gown (hit the thrift store), cinch it up around your bodice and stick a sword down your back
You can wear any shirt underneath, as all medieval women did (model's hands are bare in the photos just for appearance).
Occassions: Satin prom dresses for teens is perfect as prom dresses, formal dresses, cocktail dresses, evening party dresses, ball gown, bridesmaid dresses, mother of the bride dresses, quinceanera dresses, homecoming dresses, pageant dresses, baby shower dresses, princess prom dresses, maxi dresses, perfect for wedding, prom, reception, gala, red carpet, juniors party, cocktail party, beach party, birthday party, engagement, graduation, ceremony, sweet 16, banquet, carnival, masquerade ball, night club, going out, dinner, photography, holiday, Christmas, black tie event, any formal and semi-formal occasion