A barrel is a container item which can hold various items that has appeared in all three games of the Super Smash Bros. series. This makes it similar to a crate. When one picks up a barrel, because they are so heavy, one will not be able to jump, attack, and one will move very slowly while holding it (with the exception of Donkey Kong). After one has picked up a barrel, one can throw it up, forward, or down. If a standing barrel is hit with a weak attack or lands on a sloped surface, it will roll across the stage.
 Super Smash Bros.
In the original Super Smash Bros., the player cannot move while holding a barrel, unless they are playing as Donkey Kong. Interestingly, Donkey Kong can not throw Barrels below him. There is a 12.5 chance barrels, crates, and capsules will have explosives, so it is a good idea to throw them so they won't come back and possibly explode on the player.
 Super Smash Bros. Melee
In Super Smash Bros. Melee, barrels can also very rarely release an Adventure Mode enemy, such as a ReDead, an Octorok, or a Goomba. When they are thrown at opponents, they can deal 18 to 22% damage and good knockback. When they explode once they have hit an opponent, they can deal around 45% damage and strong knockback. They contain only one item.
 Super Smash Bros. Brawl
In Super Smash Bros. Brawl, barrels, along with Crates, have a different appearance depending on what stage the player is playing on. On a more futuristic stage, e.g. Lylat Cruise, they take on a futuristic appearance, and on more fantastical stages, e.g. Yoshi's Island, they look like wrapped-up presents. Barrels also fly much farther and faster when struck. Additionally, if a rolling barrel comes to a rest, it stops being harmful to players and can be picked up a re-thrown, or attacked to send it flying/break it.
 Damage throughout the series
In Donkey Kong, Donkey Kong would roll barrels at Mario. If Mario got hit by the barrels, he loses a life. Barrels also appeared in Donkey Kong Country. There is an enemy in Donkey Kong Country called Manky Kong that throws barrels at the player. If the player or his team mate gets hit by a barrel, the person who got hit runs away leaving the other player. There are also barrels that can be picked up and thrown at enemies. In Melee and Brawl, the barrels contain items and they can be thrown at other players to cause damage or even a KO. 
 Description from the Super Smash Bros. Instruction Booklet
Attack it or pick it up and throw it to break it open and release its contents.
 Melee trophy
 Brawl trophy
 See also