<P> Olson is also a writer, contributing a section to the best - seller Adventure Time Encyclopedia and an upcoming book for Cartoon Network . </P> <P> Olson has appeared as a singer and actress on television shows and in live theatre, including Comedy Central Stage, the HBO Theater, The Fake Gallery, and the Disney Channel series Phineas and Ferb . Olson has also appeared on The Tracy Morgan Show and guest starred on The Ellen DeGeneres Show singing with DeGeneres, actor Jack Black and Broadway star Kristin Chenoweth . She is currently a cast member and singer on two animated series: Cartoon Network's series Adventure Time, playing Marceline the Vampire Queen and on Disney's animated series Phineas and Ferb playing Vanessa Doofenshmirtz, the sarcastic daughter of the evil Dr. Doofenshmirtz . In Adventure Time, her father, Martin Olson, plays Marceline's dad Hunson Abadeer and Marceline sang a short song about him eating her French fries . She also sings a number of songs in Phineas and Ferb, including the duet "Busted!" with Ashley Tisdale as well as popular solo songs, including "I'm Me," "Not So Bad a Dad After All," "I'm Lindana and I Wanna Have Fun," "Happy New Year" and many others, including her song in the Phineas and Ferb Christmas Vacation special "Got That Christmas Feeling ." She has written songs for Phineas and Ferb and has written and recorded her own songs with renowned music producers Rick Nowels, Camara Kambon and Hollywood jazz great Rob Mullins . </P> <P> Olson rose to fame for her role as Joanna Anderson in the 2003 holiday film Love Actually, singing the song "All I Want for Christmas Is You ." Her singing was praised, with director Richard Curtis stating in the commentary in the music section of the Love Actually DVD that Olson's singing was so perfect, they were afraid the audience would not believe that a ten - year - old could really sing the way she did and would assume she was lip - synching to Mariah Carey's voice . They had to train her so her singing would sound more believable, and add the sounds of inhalations to the track . This led to guest spots on The Ellen Show, The Tracy Morgan Show and singing with Jack Black and Kristin Chenoweth . Olson also posted original songs on her YouTube account . </P> <P> From 2008 to 2015, Olson voiced the recurring character Vanessa Doofenshmirtz in the Disney animated series Phineas and Ferb along with actor Thomas Sangster (Ferb Fletcher), who played Joanna's love interest Sam in Love Actually . Her character is described as a punk goth, the sarcastic daughter of the not - so - evil Dr. Doofenshmirtz . She occasionally attempts to thwart her father's evil schemes regarding her mother, always ending in failure . Although she is a sarcastic and spoiled teenager, she also has a kind heart and loves her parents . Olson's father, Martin, was a head writer for the first season of the show, and one of the main songwriters at Disney throughout the series . </P>

Who sang all i want for christmas in the film love actually
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