One of the primary ingredients for a fantasy play is a setting in another time or place. So plays of this genre have many aspects that do not depend on realism. Other worlds are common locations for plots and characters can be from another place or non-human.
Fantasies rely on the audience’s imagination and sometimes even involve the use of magic by characters on stage. Fantasy is more common in novels than stage plays. In the theatre it is perhaps best associated with particular musicals, such as Beauty and The Beast, which involves a prince being transformed into an ugly beast by and old witch.