Recorder

A Warp Whistle is an item from Super Mario Bros. 3. Using it sends Mario (or Luigi) to the Warp Zone. From here, he can skip up from the middle of a world to the start of a later world. Using it in World 1 will allow Mario to warp to World 2, 3, or 4. Using it in a world from 2 through 6 will allow him to warp to World 5, 6, or 7. Using it World 7 will allow him to warp to World 8. If a second whistle is used while in the warp zone, then the player is taken directly to the World 8 Pipe.

There are only 3 whistles in Super Mario Bros. 3:

World 1-3
Obtained by falling through (holding down on the control pad while standing on it) the last white block in the level and making Mario's way to the end of the stage while behind the scenery.

World 1 Fortress
Obtained by flying above the level at the very end of the first area. Start all the way on the right side past the door and run to the left, taking off at the last second.

World 2 Secret Fire Bros. Brigade
Obtained by using a Hammer on the rock in the upper right corner of the map. Destroy the Fire Bros. to win it.

Trivia

 * Mystical Whistle's the name of a Sammer Guy in Super Paper Mario is a pun on Warp Whistle.
 * The song played by the Warp Whistle is from The Legend of Zelda series.
 * A reference to the Warp Whistle is made in the Nintendo Monopoly.