Note: This game is also titled Family Ski And Snowboard.
At Mt. Angrio (Ride The Mountain), enter the purple circles next to one of the helicopter launch spots (at the signs marked "1" through "6"). Press A to use the helicopter, then immediately hold B + Up to replace it with a UFO, which will take you to the other parts of the mountain.
Swing the Wii-mote at the map screen to throw snowballs at the screen. Note: This can also be done at some other screens.