The boys perform a MASH-up of "It's My Life" and "Confessions" in the episode titled Vitamin D.
Episode 8 - Mash-up
Season 1 episode 8, Mash-Up
Mash-Up - Season 1, Episode 8
If you are referring to the episode of Glee that aired on Tuesday, November 15th, 2011, it was called Mash Off.
That's Mash-up
mash-up
Rumour Has It/Someone Like You by Adele is a mash-up featured in Mash Off, the sixth episode of Season Three.
Mash up of "its my life " and "confessions"
I believe it's episode 8 - Mash-Up
Mr. Shuester
In the end of 1x06 "Mash Up"
I think it's the episode called Vitamin D (episode 6) in which mash-ups of two songs are performed by the two teams in Glee club (Girls vs. Boys). The girls performs a mash-up of Halo and Walking on Sunshine.