There is a hidden playable character exclusive to the multiplayer mode of the game. If you unlock Hard ROCK! Mode, but don't unlock Commander Kahn, Mr. X will be unlocked in both single-card and multi-card Vs. Mode where Commander Kahn should be. He appears to be Commander Kahn with a giant cat head.

In an interview with Keiichi Yano, he revealed that the designs for the Elite Beat Agents were based on the Village People before iNiS chose to settle on the FBI Agent style used in the final version of the game.

Keiichi Yano revealed in a 2007 interview that the original name for the "Elite Beat Agents" was "Disco Rangers".

In an interview with Keiichi Yano, it was revealed that they were thinking about creating a Wii version of the game.

The game was originally going to have twenty songs, but only nineteen were included in the final game. According to an article from 1UP.com, the scrapped song was "Livin' la Vida Loca" by Ricky Martin. This would be confirmed years later by video game journalist Liam Robertson in a video detailing the history of the game and its Japanese counterpart Osu! Tatakae! Ouendan. According to the video, the song was cut due to licensing issues later in development, with UI programmer Robert Ota Dieterich stating it was intended to be used in the game's second level before being replaced by "Makes No Difference" by Sum 41.