Guide Pen-Pen or his sweetheart Deda-Deda (or both in a multiplayer frenzy) around the mazes and try to crush all monsters on screen with the Ice Blocks scattered around. Use the Action button to push the ice block or crush it if it cannot be pushed.
If you face the outer wall and press the Action button then you will start breathing the icy breath onto them which will make them freeze. If there are any monsters walking by the frozen wall they will get instantly stunned and you can use this ability to crush them with an ice block. Try to spell BONUS for surprise, and rack up combo scores by killing Snow Trolls in various imaginative ways.