Story Mode is the Adventure Mode of Mario and Sonic at the London 2012 Olympic Games. It is based on Story Mode (Mario and Sonic at the Olympic Winter Games).
- Donkey Kong
- Bowser, Jr.
- Dr. Eggman
- Metal Sonic
- Dry Bowser (with Dry Bones)
- Dry Bones (with Dry Bowser)
- King Boo (with Boo)
- Boo (with King Boo)
- Jet the Hawk
- Bowser, Jr.
- Dr. Eggman Nega (with his Shy Guys)
- 3 Shy Guys (with Dr. Eggman Nega)
- E-123 Omega
- Dr. Eggman
- Metal Sonic
- Invincible Bowser
- Invincible Dr. Eggman
- Donkey Kong
- Goomba (pretending to be Mario)
- Fake Sonic
- Bowser's Minions
- Dr. Eggman's Robots
- Big the Cat
On the day before the Opening Ceremony inside Big Ben, Bowser and Dr. Eggman are upset that they are not invited to the Games. They then decide to stop the games from happening by using a color fog smoke machine to cover all over London.
A few hours before the Opening Ceremony, Toad is setting up the cones on the field when he sees a Color Fog spreading around the field. Then Mario and Sonic who are covered in Fog arrives on the field. Toad begs them for help but instead Mario and Sonic prepare to fight him. Bowser and Dr. Eggman then watch as Toad gets scared and as he falls down.
A few minutes after the events on the field, Mario and Luigi help out Toad on the field. Toad explains what happened a few minutes earlier. Behind them, Sonic and Tails who are covered in Fog arrives on the field. Toad begs them for help but Mario and Luigi stop him revealing that they are imposters. Sonic and Tails then challenge Mario and Luigi to an olympic match.
After Mario and Luigi wins, Sonic and Tails fade away which surprises the Trio. Mario and Luigi continue investigating on the Field.
A few minutes later, Mario and Luigi run into Dry Bowser and Dry Bones who are looking for Toad. Toad runs away as Dry Bowser attempts to chase after him. Mario and Luigi stop him and in order to get pass, they must defeat them in order to get pass.
After Dry Bones and Dry Bowser are defeated, Mario and Luigi find the Fog Machine and destroy it. Dry Bowser-knowing that the task was very challenging-and Dry Bones escapes from the Field. The fog in the Stadium and the Field clears out. Mario and Luigi tell Toad that their job is done until they see Fog near Hyde Park. Mario, Luigi, Toad check it out as Chao stays at the Stadium.
Meanwhile near the Ghostly Tower, Sonic and Tails arrive in London but a huge fog covers the city already. Sonic and Tails greet Mario and Luigi but find out they are imposters. They then match them in an olympic event.
After defeating them, they fade away. They continue to go the Ghostly Tower but find King Boo and Boo who try to stop them. Sonic and Tails find out where the destination of a Fog Machine is. King Boo and Boo match Sonic and Tails in an olympic event.
After being defeated, Sonic destroys the Fog Machine clearing the Fog. King Boo and Boo escape as Sonic and Tails continue their investigation on the mysterious fog.
Back at Hyde Park, Daisy and Amy look for Peach and Blaze until they are confronted by a Fake Peach and a Fake Blaze. They then try to confront them.
After the Fake Imposters are defeated, a large group of Imposters kidnap Daisy and Amy. Later on, Peach and Blaze search for Daisy and Amy. They are then confronted by a large group of Imposters. They then challenge them to an olympic event.
After the group of Imposters are defeated, Peach and Blaze save Daisy and Amy. A Toad then alerts the group of a white bat who reveals to be Rouge. Rouge challenges the group to an olympic event which they do.
After they defeat Rouge, Rouge reveals that she saw a Fog Machine when she was arriving. The group then destroys the Machine which allows Rouge to join the group. Mario, Luigi, Toad arrive to see if they are alright and continue their investigation of the mysterious fog. The group then continues finishing the invitations to the games.
Meanwhile at the Bridge of London, Yoshi is facing 2 Imposters as Sonic and Tails watch. After defeating the 2 Imposters, Yoshi gets pass the Bridge of London followed by Sonic and Tails.
Yoshi then meets Shadow and Silver and they are confronted by a Hawk named Jet. Sonic and Tails confront Jet but they are stopped by the Challengers who confront him.
After Yoshi, Shadow, and Silver defeat Jet, Jet joins their side until they hear Bowser's voice. It reveals that it was only Bowser, Jr. Then the Challengers all face against Bowser, Jr.
After defeating Bowser, Jr., Sonic destroys the Fog Machine as Bowser, Jr. runs away. Sonic and Tails then continue their investigation of the mysterious fog.
Near the library, Mario, Luigi, Sonic, Tails, and Toad finally meet together but a group of Imposters attack the group. The Heroes then face off the Imposters.
After defeating the Imposters, they continue their mission inside the Library. Tails finds out that William Kidd stole a fog machine 300 years ago. They then split up as Espio and Charmy arrives to help out.
They are later confronted by Dr. Eggman Nega and his Shy Guys who challenge the Group to an event. After defeating him, he escapes as they destroy another Fog Machine. They then agree to split up once again.
Meanwhile at the Tennis Court, Waluigi is using his binoculars to find a challenger to challenge him in an olympic event. Later on, 2 Shy Guys confront him but he tells them to move along. Metal Sonic eventually bumps into Waluigi on purpose breaking the binoculars. Waluigi gets upset and challenges Metal Sonic.
After defeating Metal Sonic, Metal Sonic runs away and Waluigi follows him. Wario is later facing Dr. Eggman in a Olympic Event where Wario wins. Wario attempts to destroy the Fog Machine but hurts himself since it was only a telegram. Dr. Eggman is guarding the real Machine.
Later on, Waluigi and Wario meet each other and face off Dr. Eggman and Metal Sonic. They are both defeated and Wario and Waluigi destroy the machine. Dr. Eggman and Metal Sonic then run off. Mario and Luigi and Toad then congratule Wario and Waluigi.
Meanwhile in the Wrestling Stadium, E-123 Omega knocks Donkey Kong's banana onto the floor on purpose. Tails arrives and force Donkey Kong and Omega into a Wrestling match.
After Donkey Kong wins, Omega is disconnected. Tails finds out that Omega's hard disk was replaced and he puts back the real hard disk which makes Omega good again. Tails then decides to Omega with him.
Sonic is walking in the Volleyball Court until Bowser almosts crushes and kills him. Knuckles and Vector then challenge Bowser in an olympic event.
After Bowser loses, he escapes as Sonic destroys another Fog Machine. Sonic, Tails, Omega try to find Mario, Luigi, Toad, Charmy, and Espio.
Later on, Toad recieves a call from Chao that there are only 2 places with fogs, Big Ben and Stonehenge. They meet up with Sonic's group and team up again.
They go to Stonehenge who they go to confront Imposters again. After defeating them, they find Bowser's minions and they challenge Magikoopa in a BMX match. After losing, the Bowser's minions vanish away. Omega accidentaly bumps into Big who gives the group advice on where Big Ben is.
They finally arrive in Big Ben but realize it is too late. Bowser and Dr. Eggman are invincible and Mario and Sonic challenges them into 4 Olympic Events.
After being defeated, Sonic and Mario stop the Fog Machine and Bowser and Dr. Eggman are comforted. They were in the Game List but their invitation was delayed. They then bring them to the Stadium as the Opening Ceremony begins.
After the events of the defeat of the bad guys and before the events of the Opening Ceremony, Bowser, Jr. accidentaly arrives in Stonehenge instead of London and challenges Yoshi who is training.
After defeating Yoshi, Junior challenges Silver and Shadow who are also defeated.
Bowser and his minions later try to find Mario but run into the Wild Ones who are defeated by Bowser. At the Tennis Court, Magikoopa transforms Goomba into Mario so they can fake the match.
Inside Big Ben, Dr. Eggman and Metal Sonic are training. They also see Waluigi training so Metal Sonic challenges him and Wario and beats both of them. Dr. Eggman then challenges an imaginary Sonic to an Olympic Event.
Back at Hyde Park, they are about finished invitations until Daisy wants to go to the store. Amy wants to follow and also give Sonic his invitation first eagerly. Peach wants to give it to Mario first but doesn't really care. Amy and Daisy and Peach and Blaze deal and they challenge each other.
Peach and Blaze win and they continue making invitations. Bowser and Dr. Eggman arrive in Hyde Park and agree to kidnap Peach and Blaze since their invitations are not ready. Peach and Blaze overhear this and challenge them.
After Bowser is defeated, Peach and Blaze reveal to them that they don't have to get invitations to go to the Olympic Games. They are also invited to the Games and the real Games begin.