Walk-ons – we can enter a two player scene in progress as another character, offering a move that contributes to the progression of the game(s) at play. Two high school boys are feeling self conscious in the hallway so Player 3 enters as a mean girl to point out their foibles. Two players are arguing over the value of the movie they just left, so Player 3 enters to agree with one of them and rile the other. If there is one tertiary move an improviser knows, it’s the Walk-on.
Unfortunately, too few improvisers know to Walk Off. You’re a tertiary character; the scene’s not about you. A Walk-on should only be used to heighten/sharpen a game already at play. An entering character must acquiesce to those already on stage and strive not to be the focus of the scene.