The Beam Sword (ビームソード), also referred to as Saber, is a long-range "battering item", similar in appearance to a light green lightsaber. It appeared in the entire Super Smash Bros. series; over time, its appearance gradually changed into that of a lightsaber.
The Beam Sword is referred to as "Saber" in Super Smash Flash, the reason for this change is unknown but this may be a simple mislead. Its design is based on the Beam Sword from Super Smash Bros. Melee. As with other bettering items, the Saber has a limited use and will disappear after a certain amount of uses.
For the reboot, Super Smash Flash 2, the Beam Sword is properly called by its correct name this time. Moreover, its design however has been changed to be completely unique and original to the game to carry a gray hilt and luminescent green blade. It can be used in the following ways:
Melee attack: The player can simply press the standard attack button to attack the opponent with it (7% damage).
Dash attack: The player performs this in the same way as they do a normal dash attack (7% damage).
Smash attack: This charges the power of the Beam Sword (21% damage). It might also change length to gain range.
Throwing: The Beam Sword can be thrown at opponents to increase damage (run + throw = 13% damage, throw = 7% damage).
There is no specific game whom the Beam Sword seems to originate. Instead, the Beam Sword seems to be based on the lightsaber from the Star Wars franchise, which first appeared in the original 1977 film Star Wars - Episode IV: A New Hope and has since appeared in every Star Wars movie, and almost in every Star Wars media, since then. It is presented as the de facto weapon of the Jedi and the Sith, both of whom can use them for close combat, or to deflect blaster bolts. A well known trait of a lightsaber is its distinctive hum when it is ignited, which rises in pitch and volume as the blade is moved rapidly through the air. In the SSF games, the Beam Sword present a similar humming that can be heard whenever it is swinged, though it sounds more like static electricity. The name "lightsaber" might have been the reason the Beam Sword got mislabeled as "Saber" in the original SSF.
The Beam Sword from SSF2 resembles even more the lightsaber from the Star Wars franchise than the Beam Sword from SSF and the SSB games. The green blade has the same color as the lightsabers used by Jedi Masters.