Supply guests with party masks, or have them decorate their own by supplying them with basic masks for decorating, glue guns, and accessories such as feathers, sequins and gem stones.
Turn craft time into a contest and have judging for the best mask in various categories such as Most Comedic, Most Tragic, Best Personality, etc.
Have a theater trivia contest. Use resources such as the encyclopedia or wikipedia to put together questions about theater from ancient Greece to Broadway! Have a special prize set aside for the guest who gets the most questions correct.
What could be better for this theme than charades!? Have guests show of their dramatic ability and divide evenly into teams. For an extra-thematic touch, have the clues be plays or famous theater characters.
Check out the rest of our Comedy & Tragedy Party TipZ and tell us your ideas!