Bubble

Bubbles are spherical, clear, floating objects that appear throughout the Mario series of games. They are similar in appearance to the bubbles found on Earth, except that they are much more durable, are considerably larger, and sometimes have contents within them.

Super Mario Land 2: 6 Golden Coins
Bubbles first appeared in Super Mario Land 2: 6 Golden Coins, where they were referred to as Soap Bubbles. Appearing only in one level, Mario could ride around in them.

Super Mario World
Bubbles then appeared in Super Mario World, where they can be found floating around in a few levels. Bubbles contained either power ups or enemies, usually Bob-ombs or Goombas. Simply touching a Bubble will cause it to burst.

Super Mario World 2: Yoshi's Island
In Super Mario World 2: Yoshi's Island, Bubbles had a number of roles. They sometimes house 1UPs, but usually appeared in the form of Morph Bubbles. If the player is hit by an enemy, Baby Mario will float away in a Bubble. Bubble Dayzees and Barney Bubbles also spit out Bubbles as their attack. These Bubbles can not hurt a Yoshi directly, but are capable of knocking him back. Yoshis can also bounce up high after jumping onto these Bubbles.

Super Mario 64
Bubbles can be found in the underwater levels of Super Mario 64. They usually appear when Mario opens a Treasure Chest underwater, and contain oxygen that will refill his health bar. This ability of bubbles reappears in the later game, Super Mario Galaxy.

Diddy Kong Racing
In Diddy Kong Racing, Bubble traps can be set if a player has collected three green Balloons in succession. Hitting a Bubble trap will stall whoever hit it for a fair bit of time.

Yoshi's Story
In Yoshi's Story, Bubbles called Bubble Pops held a number of objects, usually Fruit. However, these Bubbles are fairly dense, and require an Egg in order to penetrate, although jumping atop of one repeatedly will eventually pop it.

Paper Mario
The Bubble Plant of Flower Fields in Paper Mario is capable of blowing Bubbles, provided Mario brings it a Bubble Berry first. Mario must then ride the bubble across a bramble patch, which he otherwise cannot cross.

Super Mario Bros. 3
The Game Boy Advance remake of Super Mario Bros. 3 has a single Bubble that can be found in the World-e level Vegetable Volley. It houses a Super Mushroom, and can only be penetrated after the player hits it with three Vegetables.

Yoshi's Island DS
Bubbles appear throughout Yoshi's Island DS, and serve the same purpose as they did in the original Yoshi's Island.

Super Mario Galaxy
In Super Mario Galaxy, Bubbles have two roles. They can be found throughout underwater areas, and will refill Mario's oxygen meter if he touches one, much like in Super Mario 64. There are also Bubbles that can be found on land, which Mario can enter and ride around in. The player must use the Wii Remote to aim the Bubble in the desired direction, and blow it around by pressing the A Button.

Trivia

 * In Mario Party 5, there is a Capsule referred to as the Bubble Capsule. However, the Bubble Capsule contains what appears to be a Podoboo. As such, the Bubble Capsule was probably misnamed, similar to the Magikoopa Capsule.