"Fever" is a musical theme composed by Hirokazu Tanaka for the 1990 game Dr. Mario. It has since made an appearance in every Dr. Mario game to date (not counting the Gamewatch Boy version). In the original Dr. Mario, it is one of the two selectable themes, with the other being "Chill." Compared to "Chill," "Fever" is more upbeat and fast-paced.
In composing "Fever," Tanaka's aim was to heighten the various feelings players experience while playing a game, such as confidence and anxiety, by incorporating different elements into the music, creating a song consisting of "'fun' parts and 'looming dread'-type parts." He also intended "Fever" to be "different" and "unusual" as games began to evolve and the industry began to see "really serious" composers. Tanaka describes "Fever" as a "cute" song to reflect the game's tone.
"Fever" was adapted for Dr. Mario for the Game Boy, and later received updated arrangements in Tetris & Dr. Mario, Dr. Mario 64, Dr. Mario & Puzzle League, and Dr. Mario World, with Dr. Mario 64's rendition being reused in Nintendo Puzzle Collection. Another arrangement closely resembling that of Dr. Mario 64 was created for Dr. Mario Online Rx, and was later reused in Dr. Mario Express, Dr. Luigi, and Dr. Mario: Miracle Cure. All aforementioned arrangements are faithful to the original theme, with the exception of Dr. Mario & Puzzle League, whose version omits the theme's second half as well as the "responses" in the first half. In Dr. Mario Online Rx, another, less faithful arrangement plays in the Virus Buster mode.
In the Virus Vid video series promoting Dr. Mario World, another arrangement of "Fever" is used as the background music. In July 6's episode, the first eight bars were given English and Japanese lyrics, with the viruses performing.
"Fever" also makes an appearance in the form of an arrangement in Super Smash Bros. Melee as the alternate song for Mushroom Kingdom II, simply titled "Dr. Mario" and arranged by HAL Laboratory composer Shogo Sakai. It reappears in Super Smash Bros. Brawl as a selectable song for the PictoChat stage (titled "Dr. Mario (Melee)"), Super Smash Bros. for Nintendo 3DS for PictoChat 2, Super Smash Bros. for Wii U for Flat Zone X, and Super Smash Bros. Ultimate for every Mario-series stage (now under the original theme's title, "Fever"). An orchestrated arrangement is also featured in the soundtrack Super Smash Bros. Melee: Smashing...Live!
A techno arrangement of "Fever" is used for the stage "Deep Freeze" in Dance Dance Revolution: Mario Mix.
Outside of the Mario franchise, a much calmer and slower-paced arrangement plays in the hidden Virus Buster minigame in Brain Age 2: More Training in Minutes a Day! According to the game's host Dr. Kawashima, the music is intended to enhance the relaxation aspect of the minigame. This arrangement returns in the mode of the same name in Dr. Luigi and Dr. Mario: Miracle Cure.
Virus Vid version lyrics
Lyrics sung by Red, Yellow, and Blue are colored in their corresponding colors, while lyrics sung by all three are colored black.