The DLC Pack Add-on for Rock Band 3 has 12 achievements worth 250 gamerscore.
Play a downloaded song.
Earn 5 stars on Vocals on a downloaded Queen song.
Beat all of the free downloadable songs for Rock Band.
Beat 5 downloaded songs.
Beat 12 downloaded songs.
Beat 20 downloaded songs.
Play a downloaded Queen song.
Download and play three songs from a band that has Harmonix team members in it.
5 Star any Boston song.
Melt faces by beating any three '80s Metal songs.
Beat 5 songs from any band that has had Dave Grohl as a member.
Get a 200 note streak on "The Perfect Drug".