From the Super Mario Wiki
In Super Smash Bros. and Super Smash Bros. Melee, Flamethrower is the move used by Charizard as a Poké Ball Pokémon. It is also used by Charmander when it appears on the Saffron City stage in Super Smash Bros.
In Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS / Wii U, Flamethrower is Charizard's neutral special move as a playable character. Similar to Bowser's Fire Breath, Charizard spits a stream of fire from its mouth for as long as the player holds down the special attack button, but it becomes shorter and weaker over time. The direction of the stream of fire can be adjusted by tilting the control stick.
Super Smash Bros. for Nintendo 3DS / Wii U also give this move two custom variants: Fire Fang and Fireball Cannon. Fire Fang, also a move from the Pokémon games, breathes a continuous short stream of fire that hits more quickly and ends with a bite attack that deals higher damage and knockback, while Fireball Cannon breathes fireballs that travel further and do not get much weaker, but deal less damage overall. Finally, Charizard also uses Flamethrower while using its down throw.