When Romeo protests, ‘I dreamt a dream tonight’ as a gloomy reason for his not attending the party of his enemy, Mercutio launches into his famous ‘Queen Mab’ speech, criticising the honesty of any dream and the good qualities of all dreamers. The speech creates vivid imagery in the reader’s mind, which reflects Mercutio’s tremendous imagination.
‘Peace, peace, Mercutio peace’- Romeo interrupts Mercutio through his Queen Mab speech. This shows that Mercutio is very talkative. With the speech, Mercutio aims to urge Romeo to take an honest look at him.
After the party, Romeo avoids his friends and climbs Juliet's orchard walls. Mercutio calls after Romeo, teasing him about Rosaline, who he believes is still madly in love with. Mercutio cannot help but to reduce such lovesick feelings to a rude and witty sexual comment – ‘Now will he sit under a medlar tree, and wish his mistress were that kind of fruit’. Mercutio shows that he can't take anything seriously. We are left with the feeling that Mercutio has never really been in love.
There are different dynamics with Benvolio and Mercutio. Benvolio loves peace. Mercutio loves to argue. Mercutio loves to quarrel. He's naturally argumentative and in his final appearance (his death scene) it is a mixture of comic language and dramatic sadness. Mercutio is in a bad mood because Romeo isn't around. Mercutio is disapproving of Benvolio's lack of wit - he can't participate in witty banter. In Act three, scene one, Mercutio is hot and bothered and picks on Benvolio, trying to wind him up. He says, "If I argued like you argue, I'd be dead within half an hour" which is daft, because all you ever see Benvolio do is make peace. Mercutio is clearly doing what he does best - he's being difficult. His temper leads to his death Mercutio is an excellent swordsman and unlike Tybalt does not fence by the book but is more spontaneous. He dislikes people like Tybalt who are self-opinionated and Mercutio makes that clear in Act Two, Scene Four – ‘ The pox of such antics, lisping, affecting phantasimes’.
When Romeo refuses to fight with Tybalt, Mercutio jumps to Romeo’s defence thinking that he was afraid of Tybalt. He was brave doing this, as he knew that Tybalt was an experienced swordsman. When Romeo tries to break up the fight Tybalt stabbed Mercutio under Romeo’s arm. As Mercutio dies, he declares "A plague on both your houses," since he is only a friend of Romeo's and not his kinsmen.
Romeo thinks the wound is not bad, to which Mercutio replies, "No, 'tis not so deep as a well, nor so wide as a church-door, but 'tis enough, 'twill serve. Ask for me to-morrow, and you shall find me a grave man". This shows that Mercutio is still amusing even when he is dying. To die as love's victim, as it were, when you do not believe in the religion of love just physical love, and do not even know what you are dying for, is a dreadful irony that foreshadows the terrible ironies that will destroy Juliet and Romeo as the play concludes.
I think Mercutio was killed off in the play because in the first part of the play, Mercutio steals the play with his imagination and wit therefore he needed to be killed off in order for the play to belong to Romeo and Juliet.