The last DLC packs for New Super Mario Bros. 2 includes "The Impossible Pack." I think it literally might be impossible to complete as regular Mario. Doing it as White Tanooki Suit Mario makes it easy and you can earn more coins while doing it. So trying to do it as regular Mario is pointless. Even if you somehow succeed and save it as your Coin Rush record, anyone who receives it as a StreetPass can beat it using White Tanooki Suit Mario.
Oh well, that saves me from wanting to beat it as regular Mario and driving myself crazy.