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Jet Hammer is King Dedede's down special move in Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS / Wii U. When used, by holding down the special attack button, King Dedede charges up a jet-powered hammer swing; the attack gets stronger while the player charges, and the player is able to hold the charge indefinitely and move while charging, though a fully-charged Jet Hammer also damages Dedede for every second he holds it, though it stops damaging him at 150% in Super Smash Bros. Brawl and 100% in Super Smash Bros. for Nintendo 3DS / Wii U.
In Super Smash Bros. for Nintendo 3DS / Wii U, this move is also given two custom variants that can be unlocked:
Armored Jet Hammer grants Dedede super armor while charging, but it causes Dedede to take more damage than normal when it's fully charged. It also deals less damage and knockback, making it less effective at making KOs. Additionally, Dedede suffers from a longer start-up and ending period upon releasing the attack. Because of those flaws, Armored Jet Hammer's overall usage is highly impractical, despite of the included super armor.
Dash Jet Hammer enables Dedede to travel forward when he releases the move, but he does move backward a little while charging. The move deals less damage and knockback overall, but its knockback is better than that of Armored Jet Hammer.