The original game just had big Mario and fire-breathing Mario. I was honestly content with the addition of Raccoon Mario, and then the game had to bust out Frog Mario and Oh-My-God-There’s-Medusa Mario.
But then we get to some random middle-of-the-road level in Sky World. And there’s Goombas just hangin’ out in shoes. And after coming down from the ‘shrooms bender you tentatively jump on one, killing it and finding yourself with a brand new shoe. You literally become indestructible while in it, unless you commit suicide by jumping down a bottomless pit.
I, along with several million other kids, clamored for Kuribo’s Shoe to be in more levels. But that really would have killed its charm.
Death By Troggles 
I loved that stupid thing too. It’s so strange that they’d put together an all-new mechanic for a single level’s use.
Isn’t it? There was absolutely nothing special at all about that level, but they built an entire powerup for it (and even reference that powerup in one of Peach’s letters). The whole thing is just sort of loony.