From the Super Mario Wiki
Dream Hurdles is a Dream Event that appears exclusively in Mario & Sonic at the London 2012 Olympic Games. It is set in Battlerock Galaxy from Super Mario Galaxy. The starting Olympic record is held by Luigi at 119 points.
In this event, players move around a spinning Topmaniac's Saucer with the character in first showing on a screen. To earn points, players need to jump over hurdles and rivals. Players can leapfrog rivals to remove a point from them. While traveling on the saucer, players can encounter ? Switches that can change the speed or give an item. If it is a Green Shell, two appear and can be kicked. If a Green Shell hits someone, they lose five points. If it is a Super Star, the player becomes invincible and can gain points by simply running into their rivals.
The Leapfrog Artist challenge is achieved by leapfrogging another player a number of times in this event. The criteria for unlocking each achievement are as follows:
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