Wish Races are unlockable race challenges against T.T. that appear only in Diddy Kong Racing DS. They replace the Battle Stages of the original version and take place behind the Wish Door in each of the first four world hubs. The player can enter these challenges by unlocking the Wish Door with its corresponding Wish Key. Cars are the only vehicle that T.T. and the player can race in.
In Adventure mode, upon entering a Wish Door, the player is greeted by T.T., who was trapped behind a Wish Door in each world by Wizpig. Players can free T.T. after they win against him in a Wish Race. T.T. instructs the player to design a custom race track with the stylus. The player is required to draw it as indicated by the lines on the bottom screen and then pinpoint the finish line location. The player's racer and T.T. begin the Wish Race after the location was designed. It takes place high up in the clouds, where it is mostly colorless and mostly devoid of scenery and obstacles. Wish Races feature a slightly translucent, white path, with small clouds appearing as they race by. The ground surface can be seen from far down the racetrack. The racer and T.T. are both susceptible to falling off the track, especially in bumpy or tight turns. However, they are automatically redirected to the position in which they fell off from. Weapon Balloons are also found in random parts of the stage. Upon completing the race, the player receives a piece of the T.T. amulet. T.T. also walks around the associated world's lobby afterward.
There is a "Wish Race" mode option from Taj's Wishes Menu that the player can buy for fifty Coins to design custom Wish Race courses from the main menu. Wish Race mode allows the player to freely use the stylus to design a race track. There is a rainbow ink meter, which gradually depletes as the player draws the track, and they cannot continue designing their outline when the ink runs out. The track must be designed in a closed shape, so lines cannot overlap while being drawn. There is a slider on the menu that can determine how bumpy the terrain comes; it becomes more bumpy if they player slides it upward, or more smooth if slid downward. The player can also touch an erase icon to reset the field where the outline is drawn. After the Wish Race is designed, the player decides on the finish line location and then tap the check mark icon to begin the race. The race course is then saved in the game's data, but only a limited number can be saved. The player can tap the Load button to modify or race again on previously designed Wish Races.