Fireball

Fireball is Mario and Luigi's special move in SSBGA. Mario and Luigi toss fireballs with a color equal to their attire. These small projectiles deal minimal damage as they travel across the trajectory. There are several differences, though. Mario's version is affected by gravity, is weaker, and faster than Luigi's, his fireball speed has been increased, thus, he is able to hurl 4 fireballs appearing simultaneously one-by-one. This is favorable to combo larger characters. Luigi's fireball travels in a straight projectile, it is slower, and more powerful, like Mario, his speed for hurling fireballs is slightly increased.

Origin
In Super Mario Bros, when Mario or Luigi acquire a Fire Flower, they will change clothing color and gain the ability to hurl fireball projectiles at enemies. Luigi's actual fireball shares the same statistics as Mario. In Brawl, it is one of their alternate colors when they are in their fire form in the mentioned game.

Also in Mario Bros, there are red and green fireballs that occasionally appear on the stage as obstacles. Their abilities are similar to their projectiles they shoot in SSBGA, though Luigi's is identical.