It is functionally identical to Fox's Reflector: it envelops the Mii in a barrier which reflects projectiles and deals slight damage and knockback on startup. The reflector multiplies damage and knockback by a 1.5 multiplier. When reflecting projectiles at the last second, the Mii Gunner sidesteps as the projectile is being reflected.
While the move retained its original function in Ultimate, its appearance was significantly altered: the Mii Gunner now plants their arm cannon to the ground and surrounds themselves with two revolving hexagons. In addition, the move's endlag has been reduced and the Gunner has gained the ability to stall in mid-air by using it. However, any further midair uses will induce a fastfall.
Special Move customization was added in Super Smash Bros. 4. These are the variations: