I was a fairy and GK was a unicorn. unicorn.jpg
One girl got crazy with her sewing machine and a hot glue gun... Her and her horse were ravers. They had those furry leg covers ravers wear and lots of fluro beads glued everywhere... Browbands, nosebands, reins, stirrup irons. Her horse had a fluro orange furry saddle blanket, she had a fluffy helmet cover.
Some some ideas... indians, a bride and a groom, Batman and Robin, soccer players, Lady Gaga, Harry potter and ron/hermione, your horse as a garden (fake flowers sewn onto a rug) and the rider as a bee, some of the members of KISS, ballerinas, a ringwraith (Fancy Dress Friday - Lord of The Rings Ringwraith - Horse Sense