Bigger Boo

Bigger Boo was the boss of World 2-4, the third castle in Super Mario World 2: Yoshi's Island. He started as a regular Boo, until Kamek enhanced him with magic, making him grow to colossal proportions. Despite his great size, Bigger Boo was just as shy as any other Boo, and would cover his face if looked at. However, he also turned transparent when looked at, meaning he could not be attacked. To defeat him, the Yellow Yoshi turned away and ricocheted eggs of a wall, hitting Bigger Boo when he was visible. Bigger Boo inflated with each egg that hit him. Also, Fangs floated all over, which Yoshi could eat for eggs. After enough eggs hit him, he exploded in a brilliant fashion, disappearing from this world.

Trivia
Bigger Boo bears a resemblance to Atomic Boo.