I’ve read about Koopas wearing Mario-masks in Super Mario World, and the pictures below look familiar (though I can’t recall if it’s because I got them in the game or saw them on the Internet).
I can’t find any direct information on how to get them other than “finishing the special world” or “completing 100% of the game”.
Does anyone know exactly what is required of the player to get the masked Koopas and when/where they show up?