What is foreshadowed by Mercutio's statement that tomorrow "you shall find me a grave man" is that by tomorrow he will be in the grave, meaning he will be dead. In Act III, Scene I, after Romeo has refused to fight Tybalt, Mercutio takes Romeo's place and is stabbed by Tybalt. He is dying and he says in a play on words that by tomorrow they will find him a grave man. Foreshadowing is when an author gives clues about what is going to happen next.
