The controlled Ice Climber spins around like a top and travels forward a distance, with the hammer extended so that opponents take damage if they come into contact with the hammer. If the CPU-controlled Ice Climber is present, the pair will whirl around back-to-back together and the two hammers will make it so the attack hits twice as many times.
Squall Hammer can be used as a recovery move that doesn't risk separating the two Ice Climbers like Belay can, and it becomes a lone Ice Climber's only recovery move (as Belay becomes next to useless). If the special move button is pressed repeatedly while the Ice Climber(s) is/are in their spinning animation, they will rise vertically in addition to their horizontal movement, somewhat similar to Doctor Tornado and Luigi Cyclone. The vertical boost is considerably greater when both Ice Climbers are present. In Brawl, using Squall Hammer as a recovery move with a single Ice Climber will not gain any height. In Ultimate, using this in the air leaves the Ice Climbers helpless.
While the Ice Climbers have never used such a spinning attack in any of their non-Smash appearances, the term "squall" is used to define a "sudden violent gust of wind or localized storm, especially one bringing rain, snow, or sleet"; this fits the "ice-based/mountain climber" motif of the character, and can somewhat describe the Climber's action of spinning to lift themselves up into the air.
The move could be based off of Hammer Kirby. The animation of Squall Hammer looks similar to Kirby when he is swinging his hammer while he’s spinning.