Green Missile

The Green Missile is Luigi's Side Special Move in Super Smash Bros. Melee and Super Smash Bros. Brawl. It can be charged for about three seconds, and once let go, Luigi is launched sideways like a rocket, the disance and damage being based on how long he charged.

The move also has a 1 out of 8 (12.5%) chance to be a "misfire", that acts like if it was fully charged, but more powerful. It's not always beneficial, however. One possibility is Luigi charging the Green Missile and aiming at an opponent. He fires, but the misfire activates and the opponent dodges. This can very often prove hard to get back onto the stage for recovery. It also leaves the Luigi exposed to edgeguarding. In Melee, the spontaneous misfire fires Luigi extremely far. This has been toned down in Brawl, lowering the chance of a misfire SD.

For some reason, computer-controlled Luigis in Melee will always use Green Missile to recover, instead of Super Jump Punch. This may be related to the fact that Luigi's Super Jump Punch is completely vertical, with no horizontal movement, but the computer-controlled Luigis will even use Green Missile when directly below a ledge. In Brawl, lower level CPU Luigis will always use the Super Jump Punch to recover (since it can gain more horizontal distance in Brawl), but the higher level CPUs will use Green Missile to recover from far away and combine it with their double jump and Super Jump Punch.

Super Smash Bros. Brawl allows Luigi to hold this move at full charge indefinitely, and if a partially charged one hits a wall, occasionally, Luigi will get stuck for a brief moment and have to pull himself free. Also, he makes a spring noise as his body bobs up and down. Something not very well known about Luigi's Green Missile in Brawl is that it gives Luigi a slight vertical boost if used right after a jump. It's unknown why this occurs, but it could have something to do with Luigi's falling speed, which is normally slow. If this trick is used when Luigi is metal or is wearing a Bunny Hood (both of which increase a character's falling speed), that boost will be much higher.

Origin
It's unknown where this move came from, as it hasn't appeared in any Mario game released before Melee. Luigi used a move similar to this in Mario & Sonic at the Olympic Winter Games, but this game was released after Brawl and the resemblance is just a coincidence, if not being inspired by the move in Melee. Luigi has been known to have a comical style though, as mentioned on the official Smash Bros. website. It also could've come directly from Pikachu's Skull Bash or be loosely based on how Luigi fires out of the pipe canons from Super Mario World.