Onslaught is the Mii Brawler's default side special move in Smash 4. When used, the Brawler charges forward with their knee out, similar to Zero Suit Samus' dash attack. If the attack hits, the Mii Brawler will launch into a series of kicks that ends with an uppercut like Captain Falcon's Raptor Boost. The move can be used in midair to recover horizontally, but will cause helplessness that way. Fortunately, the dash won't send the Brawler over the ledge if they are on the ground. If Onslaught catches an opponent in midair, the Brawler will rise up a significant distance while attacking, and may or may not drag the opponent with them.
In Ultimate, the move has an altered animation, with the Mii Brawler throwing in a mixed barrage of punches and kicks, with the final blow being a backflip kick. It now does high knockback and damage when fresh, dealing 16% total and being capable of KOing as early as 100%. It has also received a new mechanic: Onslaught deals increased knockback as the Mii Brawler's damage accumulates, similarly to and separate from the effects of rage, but this multiplier lowers to 1x when the move is successfully used. It takes time until Onslaught's knockback multiplier returns to its increased value. A purple sparkle briefly appears on the Mii Brawler's shoes to signify when Onslaught's power returns to normal.
Special Move customization was added in Super Smash Bros. 4. These are the variations: