The Secret of the Fog
From the Super Mario Wiki, the Mario encyclopedia
The Secret of the Fog (also referred to as Heroes Episode 2 and Heroes 2) is the second Heroes 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 Mario and Sonic, and unlocks Waluigi's Ambition, Wario's Scheme, The Banana Incident and Corner the Koopa King! upon its completion. This episode's completion is required to unlock the Story Mode cleared badge.
Mario, Luigi, Sonic and Tails run off into the Phantasmal Fog, leaving Toad behind. Toad calls for them to wait for him and the group returns, with Tails apologising for leaving Toad behind. Noticing that the fog is particularly thick, the group look around for Fog machines. Toad walks into Eggman Nega while searching for fog machines, and mistakes him for Dr. Eggman, which scares Toad. Eggman Nega approaches the group, and Tails asks him if he has been causing the fog. Eggman Nega explains that he has been operating the machine as a favour for Dr. Eggman, and Tails and Toad ask him to stop it, which he refuses to do. The group then challenges Eggman Nega to an Olympic event, and he accepts, promising to show them the location of the machine if he loses.
After losing the event, Eggman Nega tells the group that they can do whatever they please with the machine before disappearing, although he does not give them its location. Toad suggests that they head in the direction that Eggman Nega came from, and the group find the fog machine. Mario and Sonic destroy the machine by Ground Pounding and Spin Dashing on it respectively, clearing up the fog. Tails suggests that they head inside the museum to look for clues, and the group goes into the museum. Tails quickly manages to find out that Dr. Eggman visited the museum and checked out a book in the library on archaeology, which describes a Fog urn that contained the Phantasmal Fog that was found at a ruin. The urn had been on display in the museum but was recently stolen, and Tails believes that Dr. Eggman had something to do with it. Espio arrives and interrupts the group, asking them to help him as Bowser and Dr. Eggman's minions have been causing trouble around London. Charmy arrives and tells the group that minions are causing trouble in four different places, and the group decides to split up and investigate separately. They all head off in groups towards different Olympic venues, with Mario and Toad heading one way, Luigi and Charmy heading in another, Sonic heading in a different direction and Tails and Espio heading off to the last venue. The group agree to meet back at the Main Stadium when they've each stopped Bowser and Dr. Eggman's minions.