Balloon Mario

Balloon Mario is a form of Mario first appearing in Super Mario World, and later appearing in Super Mario 64 DS. The former required the player to get a P-Balloon, the latter requiring a Power Flower.

Super Mario World
The form's effect is to make Mario swell up like a balloon, causing him to hover in the air. They will gradually float upwards if not moved by the player, but are capable of moving in any direction for a limited amount of time. During this time, Yoshi cannot be ridden. Mario or Luigi will start to flash when the item is about to wear off, and when it does they return to normal size and drop out of the air. The level Tubular in the Special World requires the player to continually pick up new P-Balloons to maintain flight while they make their way across the level. If Mario or Luigi pass through a Giant Gate while under the form, they will gain a bonus Super Mushroom.

Super Mario 64 DS
The form and its effects returned in Super Mario 64 DS where, on picking up a Power Flower, Mario would blow up just as with the P-Balloon and float. The control scheme for this transformation has been changed somewhat; Mario now gradually floats downwards instead of upwards, and has to be kept in the air by tapping the jump button, similar to swimming in 2-D Mario games. Once again, he flashes when it is about to wear off and plummets when it does. Mario is the only character who is affected this way when he picks up the Power Flower.

Mario & Luigi: Bowser's Inside Story
Later, in Mario & Luigi: Bowser's Inside Story, Mario can become Balloon Mario after being air-inflated. Luigi can grab onto Mario, so they can jump up and slowly float down.