From the Super Mario Wiki
Dream Alpine is a Dream Event in Mario & Sonic at the Olympic Winter Games. In order to play it, the player must reach Day 3 of Festival Mode or Day 4 of Team Festival Mode. It takes place on Seaside Hill, a stage from Sonic Heroes of the Sonic the Hedgehog series. In this event, the player must partake in an Alpine Skiing race with the addition of items. If the player passes through glowing gates or over dash panels, their speed will increase dramatically. However, unlike the regular alpine events, the player is not required to go through the gates, and the race is therefore more like Ski Cross. There are three control methods for this event, the first of which is a Wii Remote by itself. The Wii Remote can also be used with a Nunchuk attached, and the Balance Board is compatible as well.