Morph bubble

Morph Bubbles, also known as metamorphosis bubbles, are floating bubbles found in Yoshi's Island in Super Mario World 2: Yoshi's Island, its remake and its sequel Yoshi's Island DS. When a Yoshi touches this, the Yoshi will turn into a different form. Some transformations are temporary, while others last until the transformed Yoshi hits a Yoshi Block. If a Yoshi is transformed into a temporary form, it must hit a Yoshi Block to turn back to a normal Yoshi, or pop another Morph Bubble to stay in that transformation a little while longer. Also, if a Yoshi fails to touch another Morph Bubble or a Yoshi Block before the transformation time runs out, he will automatically go back to the exact location where Yoshi last touched the bubble and he will revert to his original Yoshi form.

Transformations
The transformations marked with an asterisk are not in Yoshi's Island DS.
 * Yoshi Helicopter
 * Yoshi Mole Tank
 * Yoshi Submarine
 * Yoshi Car*
 * Yoshi Train*
 * Ski Yoshi (Skis)
 * Snowball Yoshi

Trivia

 * Within the code for Super Mario World 2: Yoshi's Island are sprites for three Yoshi forms that do not appear in the game; these include a Yoshi plane, a Yoshi mushroom, and a Yoshi tree.