Burt the Bashful
From the Super Mario Wiki
Burt the Bashful (originally Burt The Bashful) is the first boss seen in Super Mario World 2: Yoshi's Island; he is found in World 1-4, Burt the Bashful's Fort. At the end of the fortress, Yellow Yoshi encounters a normal Burt, which Kamek grows to a massive size, turning it into Burt the Bashful. To defeat him, Yellow Yoshi must hit him with eggs six times; with each hit, Burt's pants continue to fall off. When he is defeated, his pants entirely fall off and, ashamed, he turns red, eventually imploding. As stated on the official Yoshi's Island: Super Mario Advance 3 website, "You can't fight while your pants are falling down!"
In volume 14 of the Super Mario-Kun, the volume based on Super Mario World 2: Yoshi's Island, Burt the Bashful is the first boss Mario, Luigi, and Yoshi encounter. He bounces around, smashing Mario in the process. Yoshi also attacks and ends up failing. An Egg-Plant assists them, but the Yoshi Eggs simply bounce off Burt. Finally, Mario, Luigi, and Yoshi grab and pull down Burt's pants, revealing his genitals. Ashamed, he shrinks and starts flying off as a deflated balloon, causing havoc to Mario and Luigi.
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