Recorder

A Warp Whistle is a rare 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 in World 7 or 8 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 the North American/European Super Mario Bros. 3. In the Japanese version of Super Mario Bros. 3, there are 4 whistles, as there is a glitch where one is located in World 5-1.

World 1-3
Obtained pressing the down button the on a white block, and running behind a black scenery.

World 1-Fortress
Obtained by running so the P-Meter is full, and flying up to a secret platform, where there is a door. The players need to press up on the once they have gone as far as they can, and a Warp Whistle in a treasure box is inside.

Note: Clearing World 1-Fortress this way will not destroy its locked door.

World 2-Fire Bros.
Players must defeat the last Boomerang Bro.. The players will then obtain a hammer, which must be used to break a block and go to a secret passage. In the passage, there is a Toad House that contains better items than normal, and a Fire Bro..

World 5-1 (Japanese version only)
In the Japanese version of Super Mario Bros. 3, there's a glitch in 5-1 which makes a random item appear at the end of the level. It can be done by flying above the stack of blocks at end of the level. After that, behind the Roulette Box, the player will notice glitched graphics. By hitting it from far left corner, the player will either earn five extra lives or a Warp Whistle.

This glitch was removed from the Super Mario All-Stars and Super Mario Advance 4: Super Mario Bros. 3 remakes, thus not allowing the player to obtain this Warp Whistle.

Trivia

 * Mystical Whistle, the name of a Sammer Guy in Super Paper Mario, is a reference to the Warp Whistle.
 * The song played by the Warp Whistle is from The Legend of Zelda series - in fact, this is based on the Recorder from the original game, complete with a Whirlwind taking the player to another location.
 * In the 2006 version of Nintendo Monopoly, the Warp Whistle is referenced in the Coin Block "Advance to Go" card.
 * Another flute is found in the game Mario is Missing!, stolen from the Teatro Colon by Koopa Troopas. Luigi had to return it to the opera house.
 * During the climax of The Wizard, Haley tells Jimmy to seek out the Warp Whistle (which she refers to as the "Magic Flute") in the World 1 Fortress, which he succeeds in doing. However, Super Mario Bros. 3 was a game that the characters had never played before, making it unknown as to how Haley even knew of the Warp Whistle's existence.