Super Happy Yoshi
From the Super Mario Wiki
Super Happy Yoshi is a special form of Yoshi that appeared in Yoshi's Story. It is activated whenever a Yoshi eats a Heart Fruit. Super Happy Yoshi is invincible, stronger, has a longer tongue, an infinite supply of eggs, as well as a better Flutter Jump. On an additional note, whenever a Black Yoshi or a White Yoshi is in Super Happy Yoshi mode, their mobility while using the Flutter Jump is increased drastically.
If a Yoshi performs a ground pound, he'll pop all bubbles on-screen, Shy Guys will be turned into the current Lucky Fruit and peppers turn into coins. Sometimes when he transforms, some coins will be revealed. While Yoshi is Super Happy, the flower, which represents Yoshi's health, laughs and is completely filled. Super Happy Yoshi's theme music is a rock remix of the current level's music.
Super Happy Yoshi only lasts for a limited time, but its effects will wear off immediately if a Yoshi eats anything like a Black Shy Guy or a Pepper or if a Yoshi is eaten by a Piranha Pest. Lastly, the form's invincibility does not protect the Yoshi from fatal hazards, such as Blue Blurps, Red Blurps, abysses, lava, and compressors.