When used, the Mii Swordfighter charges up, then launches themselves forward, somersaulting with the blade, similar to Sonic at the start of Spin Dash. If contact with the foe is made, the Swordfighter delivers a single slash, which damages and knocks the enemy back while causing the Swordfighter to gain some vertical height. Performing the move like a smash attack causes it to charge faster.
When charged to max, Airborne Assault has incredible horizontal distance, able to cover all of Final Destination, and making it great for horizontal recovery. On the other hand, careless use could easily cause self-destructs, since the move leaves the Swordfighter helpless regardless of a successful hit. In fact, fully charging the move on one edge of Final Destination will make the Swordfighter land right on the other edge (assuming no one was hit), slide off before the landing animation finishes, and fall to their doom. However, using only this will easily let you perform the Hyrule Jump.
In Super Smash Bros. Ultimate, the Airborne Assault move returns, with many changes, but it has been buffed overall. Its biggest buff is in terms of helplessness. The Mii Swordfighter won't enter the helpless state if it hits an opponent. Additionally, if the move misses and the Swordfighter goes offstage, there is a half-second window where the Swordfighter can act to bypass helplessness, but it's not very likely to go offstage with the move if used on the ground because the move stops at ledge. The fact that the Swordfighter can prevent helplessness is enough to significantly improve the Mii's recovery. An additional buff may include being safer on shield as the Mii Swordfighter will bounce back if hitting a shielding opponent. The move's only nerf is that it is no longer chargeable, but unlike Mii Brawler's Burning Dropkick, it is not that big of a nerf. Even though it no longer travels the full length of Final Destination, it is still great for horizontal recovery, as it still travels 3/4 of Final Destination (with Final Destination also being smaller in Ultimate to boot). There are other buffs to compensate for no longer being chargeable. It deals more damage than the previous uncharged Airborne Assault, and it has been given higher knockback.
Special Move customization was added in Super Smash Bros. 4. These are the variations: