Question: how did tybalt kill mercutio?
Answer: Tybalt and Mercutio draw their swords and fight. To stop the battle, Romeo steps between them and Tybalt stabs Mercutio under Romeo's arm. Mercutio's wound is fatal and he dies crying "A plague o' both your houses!" Blinded by rage over Mercutio's death, Romeo attacks Tybalt and kills him.