Bubble Baby Yoshi is a blue-colored Baby Yoshi appearing in New Super Mario Bros. U. It can blow out Bubbles if the player shakes or on when the character is grabbing one. These Bubbles are able to instantly defeat most enemies, turning them into three coins (six coins from certain larger enemies), a Super Mushroom, a Fire Flower, an Ice Flower, a Super Acorn, or a 1-Up Mushroom, which the player can collect. Whether an enemy turns into coins or a power-up boils down to chance, though coins are by far the most common. If an enemy turns into a power-up, which one is produced always depends on what current form the player is in: Small Mario and Mini Mario yield a Super Mushroom, Super Mario yields a Fire Flower, Fire Mario yields an Ice Flower, Ice Mario yields a Super Acorn, and Flying Squirrel Mario, P Flying Squirrel Mario, Propeller Mario and Penguin Mario yield a 1-Up Mushroom.

Players also have the ability to bounce on the bubbles to reach higher places. Bubble Baby Yoshi also adds a chorus to the current music, one he himself creates.

Bubble Baby Yoshis can be seen on the world map, in Frosted Glacier and Rock-Candy Mines and can be met and taken to any other course. A Bubble Baby Yoshi appears in a challenge in Challenge Mode, where Mini Mario must use his bubbles to reach the top of the stage. Also, they are found in some Red Toad Houses alongside other Baby Yoshis.

A Bubble Baby Yoshi also appears in Mario & Luigi: Paper Jam, on a collectible Battle Card alongside Blue Toad.