Those are probably intended to be fought with bowser. Also, I managed to glitch one through the floor in flopside pit for some reason. Apparently Nintendo just wanted a tough enemy and didn't put any other thought into it

Even still, Muths are stupid. I propose an Anti-Muth movement! Not really. I mean, they do give out Bone-In Cuts so its ALMOST worthwhile beating them. Even if I get game over'd by stupid MEGA MUTH!!! I was on the last level and it wasn't Count Bleck or Super Dimentio that killed me... It was Mega Muth... GRAH-GOOGLY!