Cymbal Rush is written in the key of D♭ Lydian.
According to the Theorytab database, it is the 9th most popular key among Lydian keys and the 68th most popular among all keys. The D♭ Lydian scale is similar to the D♭ Major scale except that its 4th note (G) is a half step higher. Music written in Lydian often emphasizes this difference by creating melodies that feature this note. Due to the dissonant interval between the 1st and 4th scale degrees, Lydian is less common in popular music.
See the D♭ Lydian Cheat Sheet for popular chords, chord progressions, downloadable midi files and more!