A Fireball is a attack that Mario can do from time to time. It is made of an orb of fire that can be used as a attack weapon or to destroy obstacles. Typically, one can only shoot fireballs if he or she acquires a Fire Flower allowing Mario to become Fire Mario. However, some enemies can shoot fireballs without the use of a power-up. Additionally, Mario can train himself to shoot fireballs from his hand (without using a Fire Flower), evident in Mario & Luigi: Superstar Saga for the Game Boy Advance.
Super Smash Bros.
In the Super Smash Bros. series, Mario and Luigi standard B move is a Fireball. Mario's Fireball bounces along the ground, while Luigi's Fireball (whose fireballs are green spectral flames) floats though the air.