The Grand Showdown

The Grand Showdown (also referred to as Final Episode and Final Chapter) is the last main 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 The Promise to Toad, and unlocks Junior Hits England once it is completed. This episode must be completed to earn the Story Mode 4 badge, and its completion is required to unlock the Story Mode Cleared badge.

Plot
Mario, Luigi, Sonic and Tails arrive at the top of Big Ben, where they find the fog amplifying system. Bowser and Dr. Eggman approach them, having been powered up by the Phantasmal Fog, which initially causes Tails to mistake them for imposters. Dr. Eggman explains that the fog amplifying system will cover all of London in fog and create imposters to stop the Olympic games from happening. Tails drops the walkie-talkie, and Toad calls him from the Main Stadium to update him about what is happening across the city. He, Omochao, Charmy, Espio and Omega cleared the fog from the Main Stadium, Peach, Daisy, Amy, Blaze, Rouge and the yellow, blue and purple Toads cleared the fog in Hyde Park, Wario and Waluigi cleared the fog from Eton Dorney and still plan to get their payment from Dr. Eggman, Yoshi, Shadow, Silver and Jet removed the fog from Tower Bridge and Knuckles, Vector and Donkey Kong cleared the fog from Horse Guards Parade. Upon finding out that the skies are clear once again, Bowser and Dr. Eggman challenge Mario and Sonic to an Olympic Event.

After defeating Bowser and Dr. Eggman, Tails tells Mario and Sonic to reseal the fog urn. Bowser and Dr. Eggman try to stop them, though Luigi and Tails prevent them from doing so. Sonic smashes the case containing the fog urn using a Spin Dash, and Mario uses the urn to clear the fog, before Sonic puts the lid on it and seals the urn back up again. Having lost the power of the Phantasmal Fog, Bowser and Dr. Eggman complain about not being invited to the Olympic games. Tails asks them if they wanted to join in, and the pair explain that they did but never received any invitations. Toad interrupts over the walkie-talkie, saying that Bowser and Dr. Eggman's names are on the competitor list, though they don't know what had happened to their invitations, and that they can still register if they bring their IDs to the Main Stadium. Bowser and Dr. Eggman claim to not have any IDs with them at the time, though they arrange for them to be allowed to register if Mario and Sonic will vouch for them. The group head off to register, and the opening ceremony finally happens with all of the characters from the Story Mode in attendance.

After completing the episode, the credits will play and features stills from the Opening, Stadium Blues, Foggy Foes, The Ghostly Tower, Peach in a Pinch, The Mysterious Thief, The Wind Master, Enter Bowser?!, Mario and Sonic, The Secret of the Fog, Waluigi's Ambition, The Banana Incident, Stop Dr. Eggman!, Clear Skies Again, To the Ruins! and The Grand Showdown, as well as a monochrome image of all of the athletes as well as Toad and Omochao.