Queen Mab
Early on in the play, Mercutio delivers a lengthy and elaborate speech about Queen Mab, a fairy who rides through the night bringing dreams to sleepers. Notably, Queen Mab is not necessarily a benevolent character, and is instead a symbol of mischief, manipulation, and indulgence of sleepers' vices. When Mercutio tells Romeo that he believes Romeo has been visited by Queen Mab, he suggests that Romeo is becoming too caught up in daydreams and fantasy.
Light and Darkness
One of the central motifs of the play is the interplay between light and darkness. Romeo and Juliet are consistently comparing one another to different forms of light, including the sun, the stars, and the moon, emphasizing the sense of "illumination" they get from each other. However, the light/dark imagery is not used in a traditional, moral sense in the play: light does not always indicate good, and dark does not always indicate bad. Instead, the imagery works to emphasize polarization and opposites throughout the play, highlighting the central conflict between the two families.
Poison
Poison plays a significant role in the play both literally – the poison is what catalyzes the double suicide of Romeo and Juliet – and figuratively. In Act Two, Friar Lawrence notes that poison is not an inherently fatal substance, but that it was instead made dangerous by human hands. When poison reappears at the end of the play, it becomes a symbol of this human intervention: Juliet's poison did not actually kill her, but Romeo misinterpreted what he saw and killed himself because of it.
Night
Along with the prevalence of light/dark imagery throughout the play, the nighttime itself is an important motif for the development of the plot. The arrival of nighttime is what allows Romeo and Juliet to pursue their love in secret. All of the major events of their relationship happen at night: their meeting, their pledge to one another, their marriage, and eventually their suicide. That a large portion of the play takes place at night showcases the importance of privacy in the midst of the public feud between the families.
Mercutio
Mercutio is an immensely important character in the play – moreso, one could argue, than either Romeo or Juliet – not only because he is Romeo's best friend, but because he is often a symbol of third-party criticism of both the Montague and Capulet families. Mercutio dismisses Romeo's fantastical musings outright, encouraging him to become more realistic. He also criticizes Tybalt's commitment to honor (which comes at the expense of his own life). In many ways, Mercutio can be interpreted as the "voice of reason" in the play, which is in part why his death is so tragic. Even in his dying speech, however, Mercutio warns the feuding families about the destruction that will come if they keep indulging their hatred for one another.
