Amber Riley plays Effie White in this episode during the fantasy sequence after Will threatens her with having to leave the GLEE club. She went on to win a 2017 Lawrence Olivier award for her performance as Effie in the London revival of "Dreamgirls".
Tamlyn Tomita (Julia Chang) played Kumiko in the movie The Karate Kid Part II. The character was a dance teacher with dreams to be onstage. Here she plays Mike Chang's mother who wanted to dance and never got to take lessons.
Mercedes states that she doesn't know what double casting is but during Rocky Horror Glee Show (S02E05) in which she played Frank N. Furter, the roles of Magenta and Columbia were both double cast with Brittany/Tina and Santana/Quinn respectively.
In this episode they sing the Coldplay song Fix You. Frontman Chris Martin was married to Gwyneth Paltrow who played Holly Holliday. She later would end up marrying writer/created Brad Falchuk.