Hammer (ハンマー Hanmā) is Kirby's side special move, introduced in Super Smash Bros. Melee. When used, Kirby takes hold of a hammer and horizontally swings it forwards, dealing a strong blow to enemies at medium range.
 In Melee
When used in the air, the attack takes on a new form, where Kirby swings the hammer in a vertical forward-somersaulting circle. This version of the attack strikes multiple times and can be used to slow Kirby's fall. Not only that, said midair version can be used to rack up decent damage via its wide hitbox after moves like Kirby's forward throw, regardless if it misses or not.
The sourspot from Melee's grounded version has been strengthened and is now harder to hit with. Overall, the move is one of Kirby's best KO moves.
When used in the air, Kirby swings the hammer horizontally twice, with the first hit being stronger with diagonal knockback and the second hit being a semi-spike. This version of the attack is useful against bosses, as it can deal a total of 32% damage when both hits connect, and it can be used multiple times in one jump. It also decreases Kirby's falling speed, and can aid Kirby's horizontal recovery by a small distance. However, it does not provide any distance when used without moving horizontally.
 In Super Smash Bros. 4
Kirby's Hammer is confirmed to retain its function in SSB4.
Hammer is one of Kirby's many copied abilities from his various adventures. It is often one of the most powerful ones, dealing massive damage to enemies. The hammer is almost identical in appearance to King Dedede's. The way Kirby swings his hammer is almost similar to the Hammer Flip move from the said ability (where Kirby swings upward/inwards with a flaming hammer), which is one of the most powerful attacks in the series. His midair version of the attack in Melee resembles the midair attack done with the ability.
 Description from the Melee Instruction Booklet
Swing a mighty hammer vertically in the air or side-to-side on the ground.
 Description from the Brawl Instruction Booklet
Attack with a giant hammer. The attack strikes horizontally in the air and on the ground.