From the Super Mario Wiki
Falco Phantasm is Falco's side special move in the Super Smash Bros. series, beginning with Super Smash Bros. Melee. Similar to Fox Illusion, Falco quickly dashes forward, damaging any nearby opponents. This move deals more damage and knockback than Fox's Fox Illusion, and used in midair the move meteor smashes anybody it hits. In Super Smash Bros. Melee this move does not get as much distance as Fox Illusion, but in Super Smash Bros. Brawl it travels the same distance. Like Fox Illusion and Wolf Flash, Falco can stop the move by pressing the special attack button again, though this is removed in Super Smash Bros. for Nintendo 3DS / Wii U, in which the move is instead automatically stopped when Falco reaches a ledge.
Super Smash Bros. for Nintendo 3DS / Wii U also gives this move two unlockable variants. The first is Falco Phase, which does not inflict damage but Falco cannot receive damage. The second variant is Falco Charge, which deals increased damage and knockback at the beginning of the move, but does not travel as far.