He died and laid a curse upon both houses.
When Tybalt and Mercutio fight, romeo trys to defend Mercutio but ends up having him killed. Mercutio dies from Tybalt bringing the sword from under Romeo and stabbing Mercutio.
Mercutio challenged Tybalt to a fight when there was no need to do so. Indeed Mercutio was spoiling for a fight with him from the start. When Tybalt asks if he can have a word with Mercutio, Mercutio says, "why not couple it with something? Why not make it a word and a blow?" which is about a provocative as you could get.
Mercutio starts the fight that ends with Romeo fleeing the city.
In the street.
They fight in the street, which is illegal, of course.
It was when Tybalt killed Mercutio and Mercutio blamed Romeo for it.
Mercutio does not "save Romeo" in the play by fighting Tybalt. Tybalt is about to walk away in contempt of the coward Romeo who will not fight him, and Mercutio gets involved, ostensibly to save Romeo's honour but basically just to get into a scrap. In the 1996 Baz Luhrman movie, the director has Tybalt beating Romeo when he will not fight, which does prompt Mercutio to join the fight. In that version Mercutio thinks that Tybalt will kill Romeo and that he needs to intervene to save his life. It's a more flattering read for Mercutio than what Shakespeare wrote.
It is foreshadowing that Mercutio is going to tomorrow. Grave is being used as a pun.
Mercutio is the one who decides to fight Tybalt.
Mercutio thinks that Romeo will not fight Tybalt because he is afraid of him.
Mercutio believes Romeo has become feminine after falling in love, but he quickly moves to fight Tybalt when Romeo refuses.
Mercutio encourages Benvolio to fight by saying, "O calm, dishonorable, vile submission!" He implies that it is better to stand up and fight rather than give in to dishonor and shame.