From the Super Mario Wiki
Ads keep the MarioWiki independent and free :)
Balloons are platforms that Yoshi can ride on in Super Mario World 2: Yoshi's Island and Yoshi's Island: Super Mario Advance 3. They appear Don't Look Back! and a bonus area in Beware The Spinning Logs, where they come in different colors. Stepping on one of them causes it to stop its natural rising, and using them too long results in their disappearance. They reappear with the same function in Yoshi's Island DS in levels Windblown Wilderness and Superhard Acrobatics, and again in Yoshi's New Island.
In Super Princess Peach, they always come in red, and gain magenta cheeks. They appear in Giddy Sky, and never move. If Peach stands on them, they go down slowly. If Peach jumps off of one, it rises. To make use of them, Peach has to jump repeatedly and get off before they vanish.
They also appear in Donkey Kong Land, where they are only present in Big Ape City's Construction Site Fight. The balloons rise up and down, and the player must time their jumps in order to land safely.