The Mii throws a chakram, a small, bladed circle, in the direction it is facing. In a Miiverse post, Sakurai revealed that the chakram can be stalled in the air for an unspecified amount of time, and the direction the weapon is thrown can be altered as well. In the Nintendo Digital Event of E3 2014, it was shown that a chakram will stick in the ground for a while after being repelled, whether it be via a shield or otherwise. It is unable to be interacted with if this occurs.
The Chakram is a very useful projectile, as not only can it be angled, but it can be thrown two ways, depending on how the control stick is used: Using the move as a tilt will make it slowly move forwards a short distance and deal multiple hits before disappearing. If used as a smash attack, the Chakram will fly relatively fast, hitting any opponent once while passing right through them, and disappear after a good distance. A tilted Chakram behaves normally against shields. It also can be lodged to the ground by angling it downwards, regardless of how it's thrown, as a fake-out. The Chakram's overall function is reminiscent of Ivysaur's Razor Leaf.
In Ultimate, the Chakram has been significantly buffed, as it now has a larger hitbox and deals more damage when smash-thrown. When thrown normally, it also has the ability to travel back towards the Swordfighter like a boomerang, allowing it to dish out even more hits than before.
Special Move customization was added in Super Smash Bros. 4. These are the variations: