"Mash Off" is the sixth episode of the third season of the American musical television series Glee, and the fiftieth overall. The episode was written by Michael Hitchcock and directed by Eric Stoltz, and originally aired on Fox in the United States on November 15, 2011. Special guest star Idina Menzel is featured as rival glee club director Shelby Corcoran, and she and Will Schuester hold a mash-up competition between the Troubletones and the New Directions. Santana mercilessly taunts rival glee club member Finn, who ultimately responds by publicly accusing her of cowardice in her relationship with Brittany, thereby revealing to their fellow students that she is a lesbian. Sue Sylvester starts a propaganda campaign against Burt Hummel, her chief rival in the special election for congress.

The third season of the musical comedy-drama television series Glee was commissioned on May 23, 2010, by Fox while the first season aired. It aired between September 20, 2011, and May 22, 2012, and was produced by 20th Century Fox Television and Ryan Murphy Television, with executive producers Dante Di Loreto and series co-creators Ryan Murphy, Brad Falchuk and Ian Brennan.