Jack

Jacks (also called mad springs, springs, spiked springs, I-beams, 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 75m. If Mario gets hit by a jack, he loses a life.

Due to technical limitations, jacks are absent from 75m in the ColecoVision and TI-99/4A ports of Donkey Kong.

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

Donkey Kong 64
Jacks reappear in the Donkey Kong arcade game playable within Donkey Kong 64, acting the same as in the original release.

Mario vs. Donkey Kong 2: March of the Minis
In Mario vs. Donkey Kong 2: March of the Minis, jacks appear in B2 in DK's Hideout, where they are known as spiked springs due to the spikes on their top and bottom sides. They act identically to their appearance in Donkey Kong, spawning from Donkey Kong's position and bouncing towards the girder structure below. If a Mini Mario without a shield comes into contact with a spiked spring, the Mini Mario breaks.

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 sprite of Donkey Kong 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.