DJ Earworm [1] is famous for his musical mashups, and this year's annual "United State of Pop" is possibly the best one yet. Taylor Swift [2], Katy Perry [3], Maroon 5, Meghan Trainor, and Iggy Azalea are all featured in the video. Plus, what roundup would be complete without a sample of Frozen [4]'s "Let It Go"? Even if you're not typically into mashups, this video is so impressive. Watch it below, and see if you can pick out all 25 songs within the song!