Photos and Audio: Tonight on GLEE- Adele, Lady Gaga, and More!

In tonight's episode of GLEE, Harmony (Lindsay Pearce), the girl Rachel met at the NYADA mixer, comes to McKinley High to terrorize Rachel into not applying to the program. In the epidode, the New Directions tackle "Rumor Has It/Someone Like You," "I Can't Go for That/You Make My Dreams," Hit Me with Your Best Shot/One Way or Another," "You and I" and "Hot for Teacher." Check out photos and audio from the 'Mash-Off' episode below!

Now in its third season, GLEE is a musical comedy about a group of eager and ambitious students who strive to outshine their singing competition to win Nationals while navigating the cruel halls of McKinley High. Since its debut, GLEE has become a bona fide cultural phenomenon, received prestigious honors including the Golden Globe and Peabody Award and singlehandedly made glee clubs cool again.

In addition to the regular cast, GLEE has featured guest appearances by a wide range of talented performers, including Gwyneth Paltrow (who won the 2011 Emmy Award for Outstanding Guest Actress in a Comedy Series), Carol Burnett, Kathy Griffin, Cheyenne Jackson, John Stamos, Britney Spears, Kristen Chenoweth, Idina Menzel, Jonathan Groff, Molly Shannon, Olivia Newton-John and Neil Patrick Harris, who won a 2010 Emmy Award for Outstanding Guest Actor in a Comedy Series for his work on the show.

Photo Credit: Adam Rose/FOX