Yo-yo

Yo-yos are equippable weapons introduced in EarthBound, and later reappearing in Mother 3, which raises the user's Offense. In both games they appear in they are universal weapons meaning they can be used by any of the human party members. They replace the boomerang from EarthBound Beginnings.

In EarthBound they noticeably raise the user's offense higher than most of the equips that can normally be obtained at that point of the game, however they come with a cost: they lower the user's accuracy by a bit causing attacks to miss 18.75% of the time. In Mother 3 they no longer lower the user's accuracy.

EarthBound

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Mother 3

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In the series
In all six of the Super Smash Bros. games Ness uses a yo-yo for both his and his. For his up smash Ness performs the "around-the-world" trick where he swing the yo-yo over his head, starting from the front, then finishing from the back. His down smash is the "walk-the-dog" trick and swings down from behind, then around below him and finishing in the front. In Super Smash Bros. Ultimate they have been given the ability to charge while hanging off of a ledge, which has become infamous for its strong utility as an ing technique.

Trivia

 * The friend's yo-yo is often theorized to be Ness's yo-yo due to being found in Porky's playroom and being called the "friend's" yo-yo.
 * In Super Smash Bros. Melee there is a glitch with Ness's yo-yo smash attacks where they will drop a hitbox on the ground, which allows Ness to attack an opponent from almost anywhere on the stage.