From the Super Mario Wiki
Squall Hammer is a Special Move used by the Ice Climbers in Super Smash Bros. Melee, and Super Smash Bros. Brawl. It is performed by pressing and pushing to the side. It spins both Nana and Popo around with their hammers held far out. They spin forward in the direction the Control Stick is tilted in. It deals approximately 7-19 damage. The attack is less effective if only one Ice Climber is in battle. In Super Smash Bros. Melee Popo and Nana use only their left hands to swing the mallets, as opposed to Super Smash Bros. Brawl where they use both of their hands to swing their mallets.