The DLC Pack 1 Add-on for Rock Band Blitz has 7 achievements worth 100 gamerscore.
Play at least 300 unique songs.
Play at least 150 unique songs.
Play at least 50 unique songs from the same decade.
Play at least 50 unique songs in the same genre.
Play a song from every decade since the '50s.
Play at least 10 unique songs by the same artist.
Play at least 50 unique songs.