From the Super Mario Wiki
3000m Steeplechase is an Athletics Event that only appears in the Nintendo 3DS version of Mario & Sonic at the London 2012 Olympic Games. The event is similar to the real life one it is based on, with the objective of the event as being first to finish a course with hurdles and obstacles, although it is not timed, and records cannot be achieved on this event.
3000m Steeplechase appears as the challenge of the second Challengers episode The Wind Master in the story mode, where Shadow the Hedgehog must beat Jet the Hawk. It also appears as the third part of the first and third challenges in the third Challengers episode Enter Bowser?!, where Yoshi must beat Bowser Jr. in it as well as in Triple Jump and 10km Marathon Swim in the first challenge and Shadow must beat him in it again but instead with 110m Hurdles and 1500m. It also appears as the second challenge in the second Challengers bonus episode Junior, Super Hero?, where Bowser Jr. must win it against Shadow.
The event starts with the four characters lined up on the starting line, and after a short period of time, the player must press the A Button to start the race. The initial order of the characters is decided by the order in which the button was pressed after being prompted, with pressing beforehand causing the character to have a false start and join at the back. The characters then start to follow the track around and come up to obstacles of both single hurdles, which are jumped by pressing A once, and blocks in front of areas of water, which A must be pressed twice for, one to jump onto the block and once to jump off it. If the second A button press is missed on a water obstacle, the character will trip and roll back towards the other characters. The rolling character can also be jumped over by pressing A, and will join the back shortly after they have rolled off screen. If a character fails to jump a hurdle or onto the block of the water obstacle, they will be sent straight to the back. The character who is at the front at the end of the race wins, with the other positions decided by the order of the characters behind them. There are a total of 26 obstacles on the track.
1) Start: Press the A Button.