"Mookie's Last Christmas" is a song written by Saosin

Saosin

Saosin is an American rock band originally hailing from Newport Beach, California. The band was formed in 2003 and recorded its first EP, Translating the Name, that same year with original singer Anthony Green. Green left Saosin following the band's decision to sign with a commercial label,...

's former singer Anthony Green

Anthony Green (musician)

Anthony Green is a musician from Holland, PA. He is currently the lead singer of Circa Survive, previously in the bands Saosin, The Sound of Animals Fighting, Audience of One, Jeer at Rome, High and Driving, and Zolof the Rock and Roll Destroyer.-Circa Survive:Anthony Green joined California rock...

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The lyrics are about Saosin guitarist Justin Shekoski's father, who died in a car accident. It happened on a Christmas tour, hence the title. 'Mookie' is the name of Anthony's dog.
The track was not featured on Translating the Name

Translating the Name

-Charts:Album Billboard- Credits :Band* Anthony Green - lead vocals, additional guitars* Justin Shekoski - lead guitar, backing vocals* Beau Burchell - rhythm guitar, keyboards, programming, backing vocals* Zach Kennedy - bass...

but it was included on a compilation album, A Santa Cause: It's a Punk Rock Christmas.
An acoustic version was included on Saosin's live album, Come Close

Come Close (album)

Come Close is the first live album released by the post-hardcore band Saosin. The album was released on March 11, 2008 on Capitol Records and features a live video recording of the band's performance at The Theater of Living Arts in Philadelphia, Pennsylvania on November 3, 2007, as well as a CD...

This song is a big fan favorite and there has been a lot of discussion about the lyrics.

This song was covered by Cove while auditioning for the band