Bouncy Cloud

Bouncy Clouds are cloud platforms that appear in New Super Mario Bros. Wii, New Super Mario Bros. U and New Super Luigi U. Anything that lands on them bounces very high, including enemies. Their appearance is reminiscent of Cloud Blocks, as both are white fluffy cloud featuring a smiling face in the middle.

New Super Mario Bros. Wii
In New Super Mario Bros. Wii, four of them appear in a secret area in World 2-6, and many of them appear in World 9-8.

New Super Mario Bros. U
In New Super Mario Bros. U, they appear in two levels, several of them can be found in the level Bouncy Cloud Boomerangs, and a single one is found in the final level of Superstar Road, Follow That Shell!.

New Super Luigi U
In New Super Luigi U, they are also found in two levels, Above the Bouncy Clouds, and Flying Squirrel Ovation.

Super Mario Run
As of the version 3.0.4 update, a Bouncy Cloud appears as a Kingdom Builder object in Super Mario Run. It is a 3★ reward that can be won from Bonus Games.

Mario Party 9
In Mario Party 9, Bouncy Clouds are found in the minigame Buddy Bounce, where the players bounce on the clouds to collect the most balloons.

Trivia

 * When the player is not on a Bouncy Cloud the cloud opens its mouth to match the vocals in the level.