100m Plus is a Plus Event that appears in the Nintendo 3DS version of Mario & Sonic at the Rio 2016 Olympic Games. The objective of the event is to run the track in the fastest time. The playable characters in this event are Mario, Yoshi, Nabbit, Sonic, Shadow, Metal Sonic and Mii, with Nabbit being unlocked by beating him in the event on the first day of Sonic's story in the Road to Rio mode. Toads appear as referees in this event.
At the start of the event, the player must press to stop the item roulette and randomly select an item to appear in the event. The player must then charge up by pressing and holding , and release it when "Go!" appears onscreen to start running. The longer the player charges for, the faster their speed when they start running. If the player releases the button too early, they will not be penalised but will have less time to charge up. To speed up, the player must repeatedly press , with the speed of the character depending on how quickly the player presses . During the race, the player can catch up to their randomly selected item and gain a speed boost. Each item provides different speed boosts and has different movement:
The player can also perform a Super Dash by pressing during the race, which gives the character a speed boost with a unique effect that can only be used once. If the character collects or uses an item during their Super Dash, then the remaining effect of their Super Dash is canceled and will only receive the boost from their item. The player can also press just before crossing the finish line to lean forward and finish the race with a slightly faster time. The first character to cross the line is the winner.