Junior, Super Hero?
From the Super Mario Wiki, the Mario encyclopedia
Junior, Super Hero? (also referred to as Challengers Bonus 2 and Challengers +2) is the second Challengers bonus episode in the Story Mode of the Nintendo 3DS version of Mario & Sonic at the London 2012 Olympic Games. The episode is unlocked after completing Junior Hits England, and unlocks Junior Triumphant! once it is completed.
A Chao and Omochao are being cornered by an Egg Pawn and a Flapper while a Goomba watches. Shadow and Silver arrive and confront the robots, recognizing them as Dr. Eggman's, and prepare to defeat them. Bowser Jr. arrives and falls off his Bullet Bill, landing on both of the robots and defeating them. Impressed with how he managed to deal with the robots, Silver and Shadow challenge Bowser Jr. to an Olympic Event. Although initially doubtful, Bowser Jr. accepts the challenge when Omochao suggests that doing so would impress Bowser.
Bowser Jr. manages to defeat them both, which initially appears to anger them, though the pair reveal that they were only joking and look forward to facing Bowser Jr. again. Shadow and Silver then leave, closely followed by Chao and Omochao. The Goomba approaches Bowser Jr., and while impressed by his performance, suggests that Bowser Jr. should train some more. Bowser Jr. initially refuses, though the Goomba suggests that if he managed to defeat another one of Dr. Eggman's robots, Dr. Eggman would tell Bowser about it. Bowser Jr. then sets off to find more robots, and the Goomba follows afterwards.