A number of former main characters on the show have returned for this two-part episode. These include Yale student Quinn Fabray (Dianna Agron), MIT student Brittany Pierce (Heather Morris), Noah "Puck" Puckerman (Mark Salling), who was last seen riding off to join the military, UCLA student and aspiring singer Mercedes Jones (Amber Riley), and Joffrey Ballet School student Mike Chang (Harry Shum, Jr.). Two characters played by special guest stars return as well: April Rhodes (Kristin Chenoweth), who went to Broadway to star in an original musical that won at least one Tony award, and substitute teacher Holly Holliday (Gwyneth Paltrow). A recurring character in this episode is cheerleader Becky Jackson (Lauren Potter). There is a new character appearing in the episode who is a potential Yale "love interest" for Quinn: Biff McIntosh, played by Chace Crawford. An album, "Glee: The Music, Celebrating 100 Episodes" was released with thirteen songs on it, featuring music from both this episode and the next one (its second part). The full album was released on March 25, 2014, but the six songs from this episode were made available a week early on the day the episode aired. Five of the songs are new covers of songs that have previously appeared on "Glee": the Mark Ronson and Amy Winehouse version of "Valerie" performed by Naya Rivera and Morris; Pink's "Raise Your Glass" sung by Chenoweth and Morrison; "Toxic" by Britney Spears, performed by Rivera, Morris, and Agron; "Defying Gravity" from the musical "Wicked", featuring Lea Michele, Chris Colfer, and Riley; and Avril Lavigne's "Keep Holding On" sung by Salling. The sixth song, "Happy" by Pharrell Williams, which is new to the show, features Paltrow, Chenoweth, Morrison, Riley, and Darren Criss. Suzanne Davis of "TV Fanatic" gave the episode a 3.5 out of 5 giving generally positive reviews, praising Gwyneth Paltrow's performance in "Happy" and Salling's version of "Keep Holding On" describing it "incredibly superior to the original" but gave a negative review of "Raise Your Glass" saying it had "so much auto-tune and very inappropriate for high school students". Jerome Wetzel of "Blog Critics" gave the episode a negative review“100″ has great character moments, amid lots of story flaws and inconsistencies, and an overall weak lineup of musical numbers.