Girder

Girders are construction platforms found in various games, starting with the original Donkey Kong. Most of their appearances since then have been in reference to this appearance.

Donkey Kong / Donkey Kong (Game Boy)
Girders first appear in Donkey Kong, appearing in every stage, most notably in 25m, where they are the only type of platform. In the Game Boy remake, they appear in all of these stages, as well as several stages in the game's later worlds, such as Big-City. In both games, they act essentially as a semi-solid platform that Mario can walk on.

Donkey Kong Country
During the opening cutscene of the first Donkey Kong Country game, Cranky Kong can be seen standing on a stack of girders in a black backdrop while playing the original opening theme from Donkey Kong on a phonograph.

Donkey Kong Country Returns
In Donkey Kong Country Returns, girders are the primary floor in the Factory world. In the background for the Factory's first level, Foggy Fumes, girders arranged in the zig-zagged 25m layout can be seen at one point. This pattern also commonly appears on wall reliefs throughout the temple-themed levels, along with other depictions of Donkey Kong arcade graphics.

Mario vs. Donkey Kong series
Generic girders appear in every Mario vs. Donkey Kong game. Throughout the series, they act as semi-solid platforms much like those in Donkey Kong, being red-colored in Mario vs. Donkey Kong, Mario vs. Donkey Kong 2: March of the Minis and Mario vs. Donkey Kong: Minis March Again!, and gray with rounded corners in all of the following titles. The latter are described as "gray steel frames".

This type of fixed girder is distinct from one of the series' staple gameplay mechanics, the Red Girders, which first appear in Mario vs. Donkey Kong: Mini-Land Mayhem! These can be drawn between red rivet blocks using the touchscreen to help the Minis cross gaps or reach a higher area.

In Mario vs. Donkey Kong: Minis March Again!, pieces of red-colored girders are among the objects that fall from the top of the screen when Donkey Kong slams his fists in Floor 1 Donkey Kong. Short girders appear first, followed by longer ones that are harder to avoid after DK is hit a third time. The player loses a Mini toy if a girder crashes into it.

Super Smash Bros. series
Girders appear in Super Smash Bros. Brawl, Super Smash Bros. for Wii U, and Super Smash Bros. Ultimate in the 75 m stage, based off of the original 75m from Donkey Kong, but with visible depth. In Super Smash Bros. Ultimate, this depth can only be seen when the camera is manually turned while the game is paused.

Super Mario Odyssey
Girders appear in Super Mario Odyssey, where they are seen as common platforms throughout the Metro Kingdom. They do not act as semi-solid platforms in this game, but items such as Coins and Power Moons can be found inside some of them.

Other appearances and allusions
In the manual for Donkey Kong 64, Cranky Kong hopes that a 2D level design he submitted after three minutes of planning, the "Great Girder Grapple," made it into the game as a secret level, referencing him being the original Donkey Kong from the arcade game. While no level of this specific titles appear, it may allude to how the original game can be played in an arcade cabinet found in Frantic Factory.

Girders appear in Pixels during the fight with Donkey Kong, where the main characters have to climb to the top while avoiding the barrels and fireballs. Upon arrival to the stage, girders fall down similarly to the original game, creating a path to Donkey Kong.