Ice Shells are light blue Koopa Shells that appear in the Mario Kart series. They act like Green Koopa Shells but if a driver gets hit by one they will freeze for about 5 seconds. They can be thrown backwards or fowards. Also Triple Ice Shells appear.
Ice Shells also appeared in the Mario Strikers series. They can freeze players. There is also a Giant Ice Shell as an item.
Ice Shells reappeared in Mario Kart 3DS, making their first appearance in the Mario Kart series. They act just like in the first description.