Boomerang

The Boomerang is the most powerful weapon in Link's Awakening. One hit from it will destroy every enemy. Not any enemy, every enemy. As in, if you hit one enemy with it once it literally destroys every enemy in the entire game.

Rumor has it that this was a developer tool used for testing purposes. This is clearly wrong, because it's obvious from the final product that no one tested this game at all.

The Boomerang cannot be obtained in the game proper, as it is the reward for the malfunctioning Trading Sequence. The only remaining artifact of this sequence is the Yoshi Doll found in a cave.

So-called "100% runs" of Link's Awakening (actually heavily modified glitch runs) commonly feature obtaining the boomerang, although hacking the game in this way reduces its functionality to merely stunning most enemies and destroying only small ones like bats.