Cloud Block

Cloud Blocks are semisolid blocks mainly used as platforms for bonus areas above the ground. They first appeared in Super Mario Bros. in World 2-1, in the bonus area accessed by hitting the secret beanstalk halfway in the level. Cloud Blocks have the same appearance as Lakitu's Cloud, though slightly smaller.

Super Mario Bros.
In Super Mario Bros., Cloud Blocks first appear in World 2-1, in the bonus area reached by hitting a Brick with a beanstalk. Unlike in later games, the Cloud Blocks in this game are solid.

Super Mario Bros. 3
In Super Mario Bros. 3, Cloud Blocks first appear in the sky in World 1-1, reached by flying to the top of the level with a Super Leaf. From this game onwards, Mario can pass through them from the bottom.

Giant versions of Cloud Blocks also appear in World 4.

Super Mario World
In Super Mario World, Cloud Blocks first appear in Yoshi's Island 1, where they are used to transport a 1-Up Mushroom to Mario or Luigi.

Super Mario Maker / Super Mario Maker for Nintendo 3DS
In Super Mario Maker and Super Mario Maker for Nintendo 3DS, Cloud Blocks have a new design for the New Super Mario Bros. U game style, and in every game style, they wear goggles in the Underwater theme. Cloud Blocks can be destroyed by Thwomps, Bowser's ground pound in Super Mario Bros. 3-styled levels, and Skewers.

Super Mario Run
Cloud Blocks appear in Super Mario Run, where they are platforms in Bullet Bill Barrage. As of version 3.0.4, they also appear as platforms in Remix 10's Cloud Bonus Courses. They have exactly the same appearance as the New Super Mario Bros. U style of Super Mario Maker.

Super Mario Maker 2
Cloud Blocks reappear in Super Mario Maker 2 as placeable course elements under the "Terrain" category, having the same behavior of the original game. They are available in the Super Mario 3D World game style, having a similar appearance to the Cloud Cannons from the source game, and they do not wear goggles in the Underwater theme of said game style. Aside from being able to be destroyed by the same methods of the original Wii U game, they now can be disintegrated by digging them like soft sand from Super Mario Bros. 2 by SMB2 Mario.

Yoshi's Story
In Yoshi's Story, Cloud Blocks are used as Rail Lifts in the stage of the same name. As such, they never appear stationary.

Super Paper Mario
In Super Paper Mario, Cloud Blocks make an appearance in a hidden area in Mount Lineland that is accessible by climbing up a ladder inside a hidden block. Each Cloud Block has a Coin on it and are completely in 2D; as such, Mario is unable to stand on them if he flips into 3D.

The Super Mario Bros. Movie
In The Super Mario Bros. Movie, two Cloud Blocks can be seen for a brief moment floating beside several Brick Blocks while Princess Peach is running through the Training Course.