Halloween fun...costume idea?

So I was hoping to get some ideas about a costume for my horse for a little Halloween party in two weeks. My horse is a really awesome guy with a great brain so I’m not too worried about overwhelming him with any ‘spooky’ costume (within reason) but I wanted to know if anyone had any suggestions for a “gift horse” costume…taking from the saying "don’t look a gift horse in the mouth…please if you have any ideas share them!!!