Unrequited love is a recurring theme in the play, as several characters are in love with someone who does not return their affections. For example, Viola is in love with Duke Orsino, who is in love with Olivia. Olivia, in turn, is in love with Cesario (who is actually Viola in disguise). This creates a complex web of unrequited love that drives much of the play's action and humor.
Mistaken identity is also a key feature of the play. Viola disguises herself as a man named Cesario in order to enter Orsino's service. This disguise leads to a number of misunderstandings and complications, as other characters mistake Viola for a man and fall in love with her. The mistaken identity also creates opportunities for Viola to observe and comment on the other characters, adding to the play's humor.
Overall, unrequited love and mistaken identity are two key features that contribute to the humor and complexity of Twelfth Night.