Stop Dr. Eggman!
From the Super Mario Wiki, the Mario encyclopedia
Stop Dr. Eggman! (also referred to as Tricksters Episode 3 and Tricksters 3) is the third Tricksters 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 Waluigi's Ambition and Wario's Scheme, and unlocks A Rainbow In Fog once it, The Banana Incident and Corner the Koopa King! are completed. This episode, along with the other Tricksters and Wild Ones episodes, must be completed to earn the Story Mode 3 badge, and its completion is also required to unlock the Story Mode Cleared badge.
Wario and Waluigi run into each other, and Waluigi asks Wario is he has seen Metal Sonic. Wario says that he has not, and asks Waluigi in return if he has seen Dr. Eggman. Waluigi says that he has not, so Wario decides to head off on his own. Waluigi tells Wario that there will be a reward for Wario if he helps him find Metal Sonic, planning to get the money back from Metal Sonic, and Wario then gives him the same offer for Dr. Eggman. The pair decide to search together when Dr. Eggman and Metal Sonic approach them. Dr. Eggman aggravates Wario and Waluigi. Mario, Luigi, Toad and Charmy arrive, but decide to leave Wario and Waluigi to it. Wario challenges Dr. Eggman to an Olympic Event, which he accepts, teaming up with Metal Sonic, while Waluigi teams up with Wario.
Wario and Waluigi defeat Dr. Eggman and Metal Sonic, though the pair refuse to pay Wario and Waluigi anything. Wario then heads off to find the Fog machine, angering Dr. Eggman. Wario Ground Pounds on the machine before punching it, causing it to break and the Phantasmal Fog to clear up. Mario, Luigi, Toad and Charmy congratulate the pair on sorting out Dr. Eggman, Metal Sonic and the Fog Machine. The four head back to the main stadium, leaving Wario and Waluigi to take care of Dr. Eggman and Metal Sonic.