If you blow a whistle in Mario Adventure, you’re taken to a different bonus level depending on what world you were on.
World 1: A bunch of ? blocks. There’s two Fire Flowers and two Raccoon Tails to collect, as well as some coins. Keep in mind that only one power-up can be displayed on-screen at a time, and if you hit another ? block with a power-up in it, the first one will go away.
World 2: Battle Goombas up a hill, then slide down it (use Down to slide). When you slide to the bottom, press A on the music note block, keeping your momentum, and you’ll launch right up into another music note block. Continue this 5 times and you’ll get to the top, which has better prizes; an invisibility suit or a wand.
World 7: Takes you to the key.
World 8: Lots of prizes. Two Fire Flowers, two Raccoon Suits, and a Kuribo’s Shoe to boot (pun not intended). No wand though, which is what you need to fight the many Bowsers the easy way.