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.

Mario vs. Donkey Kong series
Girders appear in every single Mario vs. Donkey Kong game. In Mario vs. Donkey Kong, they act as a semi-solid platform much like Donkey Kong. They also appear in all subsequent games and behave in the same manner for the Minis. Additionally, a special type of Girder called a Red Girder can be drawn from red blocks with rivets in them.

Super Smash Bros. Brawl
Girders appear in Super Smash Bros. Brawl in the 75m stage, based off of the original 75m from Donkey Kong, but with visible depth.

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.

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 references
In the manual for Donkey Kong 64, Cranky Kong hopes that a level design he submitted, "Girder Grapple," made it into the game as a secret level, referencing him being the original Donkey Kong from the arcade game. While this level doesn't appear, the original game can be played in an arcade cabinet found in Frantic Factory.