Jack

Jacks (also called mad springs, springs or pistons ) are obstacles that first appear in Donkey Kong.

Donkey Kong
In the Donkey Kong arcade game, jacks are constantly bouncing and dropping near Donkey Kong on 75 m. If Mario gets hit by a jack, he loses a life.

Donkey Kong (Game Boy)
In Donkey Kong for the Game Boy, jacks are now actually thrown by Donkey Kong instead of just bouncing past him. Negating them with a handstand causes them to fall off-screen like most enemies and obstacles, instead of becoming usable like barrels.

Super Smash Bros. series
In Super Smash Bros. Brawl, Super Smash Bros. for Wii U, and Super Smash Bros. Ultimate, jacks are a hazard in 75 m. The Donkey Kong sprite at the top of the screen periodically activates, and when that happens, jacks bounce from the left, acting in much the same manner as the original version. In Wii U and Ultimate, the Ω form of the stage does not feature jacks, and in the latter, jacks as well as other stage elements more closely resemble the arcade version instead of the NES version. In addition, the spring item found in these games and Super Smash Bros. for Nintendo 3DS is modeled after a jack.