Which Mario Kart game introduced Baby Mario as a playable character?

Mario Kart: Double Dash!! introduced Baby Mario as a playable character.

Released for the Nintendo GameCube in 2003, Double Dash!! expanded the series with two-character teams: one character drove while the other handled items. Baby Mario raced alongside Baby Luigi, giving both infant versions of the famous brothers their first playable appearances in the Mario Kart series.

The game is often remembered for its roster experimentation, including Petey Piranha and King Boo, as well as its distinctive team mechanics. Baby Mario should not be confused with Mario's regular appearance or with Baby Peach, who first became playable in Mario Kart Wii. Mario Kart 8, Mario Kart 7, and Mario Kart Wii all feature Baby Mario, but none introduced him.