Mercedes makes her return to McKinley High on Glee. "Wonder-ful" is the 21st episode of the show's fourth season.
Added:

Glee Season 4 Episode 21 Quotes

Kitty: Hey Crippy Longstocking, wait up!
Artie: That's offensive.
Kitty: Aw, boo hoo.

Will: Brittany's at M.I.T. touring the campus because she's got an early acceptance.
Kitty: That can't be true.

Glee Season 4 Episode 21 Music

  Song Artist
Glee cast signed sealed delivered im yours Signed, Sealed, Delivered I'm Yours Glee Cast iTunes
Glee cast superstition Superstition Glee Cast iTunes
Glee cast you are the sunshine of my life You Are The Sunshine of My Life Glee Cast iTunes