Green Fireball

A Green Fireball is Luigi's trademarked weapon in most Spin-Off games. It is identical to Mario's trademarked Fireball, except the fireballs are green. Although Luigi has used this in many games, it seems that the ability might be replaced by electricty, as seen in Mario & Luigi: Superstar Saga and Mario Strikers Charged.

Super Smash Bros. Series
Luigi used green fireballs in both Super Smash Bros. and Super Smash Bros. Melee. Although the move was called Fireball, the same name as Mario's move, it differed slightly in both appearance and effect. Luigi's fireballs were green, matching his choice of clothing, and the fireballs were not effected by gravity. This means the fireball will always go straight, and won't bounce on the ground. However, other than that, nothing else was changed. Kirby can use Green Fireballs when he sucks up Luigi.

Mario Kart: Double Dash!!
Luigi also uses green fireballs in Mario Kart: Double Dash!!. They are his special item, which can only be used by him, Petey Piranha and King Boo. It works the exact same way as Mario's Fireball item. When Luigi throws it, either forward or backwards, he will throw five green fireballs across the course, which will ricochet off walls. It will burn any player it hits, which will daze them for a small while. However, the move can ricochet back at Luigi, dazing them as well. The fireballs split apart the farther they go, making it less accurate, so it is best used when close up.

This is not to be confused with the Green Fire, Luigi's kart in the same game.

Mario Superstar Baseball
In Mario Superstar Baseball, Luigi's special move is the Green Fireball. When used while Pitching, he will cover the ball in green fire, and toss it towards the batter at incredible speeds. This makes it hard to hit the ball, as it can easily zoom right past the batter. When used while Batting, when Luigi hits the ball, he will cover it with green fire when he hits it, and it will zoom past the field at incredible speeds. If someone catches it before it lands, they will catch fire and drop the ball. If it lands, it will lose its fire, and can be picked up safely. In both ways of using the move, it works exactly the same as Mario's Fireball special move. In Challenge Mode, Luigi will only be able to use this when the item, aptly named Green Fireball, has been bought.