He loves it when you talk dirty to him.
As long as you are not acting it out from a movie or it sounds like nothing you will ever say, talk dirty. Tell him exactly what you want and how you want it done. He loves your naughty side.
Dressing up as his favourite superhero or villain is welcome.
Getting decked out in full costume can sometimes be seen as cliché and tacky. Who cares? As long as you are both enjoying the role play, go as creative and far out as you want.