What are some common traits that Mercutio Romeo and Tybalt share?

If a play is any good, the characters' personalities are hard to sum up in a Word or two because they change according to what happens to them in the play. Romeo starts off as a kind of romantic emo slacker, who mopes around doing nothing because he fancies himself in love. He ends up in the same kind of mode, when he gets all romantically suicidal because he believes that he has lost Juliet forever. But in between, he is a witty joker with Mercutio, a polite young gentleman with the servants, a passionate speaker with Juliet in her garden, a fierce warrior when he tracks down and kills Tybalt, and a calming and mature influence when he says goodbye to Juliet. He is given to romanticism and giving way to his emotions, but he keeps regretting it and trying to be more reasonable. The other three characters, being lesser characters, are more easily typified. Indeed both Benvolio and Mercutio have hints in their names as to what they are like. Benvolio's name means "good will" and we see him in Acts 1 and 3 trying to keep the peace. But he is also a good friend to Romeo, both when they are together (in Act 1) and when Benvolio protects his name in the trial after Tybalt's death in Act 3. His advocacy saves Romeo's life, at least for a while. Mercutio's name suggests that he is mercurial, full of changes, but he is really the kind of guy who never takes anything seriously. He even jokes about his death. Tybalt is just a goon, a guy who is only interested in fighting and spends his time looking for chances to fight. We really do not see any other side to his character. Maybe he had one, but Shakespeare didn't show it.