From the Super Mario Wiki
Barrels are one of the two weapons that Donkey Kong used against Mario in Donkey Kong arcade game. Since then, barrels have appeared in many other Donkey Kong and Mario games, but they are more common to appear in Donkey Kong games. Barrels can be picked up and used to attack Kremlings, Koopas, and other enemies.
In the Mario universe, barrels do not differentiate at all from those in the Real World. A barrel is made of several vertical convex staves (fourteen in the latest appearances) bound to form a pseudo-cylindrical vase, which is the barrel itself. However, in order to be sustained, four (only three in the New Super Mario Bros. games) gray metal hoops, possibly made of iron, surround the staves: two of them are each placed at one of the barrel's base, while the other are donned on the barrel's bigger circumferences. Usually, barrels do not contain anything, as they do not leave anything when broken.
Donkey Kong series
In Donkey Kong, the first threat Mario ever faces is from a blue barrel that Donkey Kong throws in level 25m. When this blue barrel rolls into the Oil Drum at the start, it will spawn a Fireball. Donkey Kong mostly throws brown barrels at Mario which the hero could jump over - once successfully passed over, a barrel will roll further and it won't represent a peril for Mario anymore (also, with every dodge, the player is granted 100 points). With the aid of a hammer, the chubby carpenter can smash the barrels, and this is going to award him 500 points.
In Donkey Kong Jungle Beat, small barrels are used to transport Donkey Kong to different kingdoms. Every barrel has a letter in front of them, with each letter spelling out the initials of Donkey Kong Jungle Beat. The D Barrel links to the Banana Kingdom, Orange Kingdom, Watermelon Kingdom, and Apple Kingdom. The K Barrel warps the player to the Strawberry Kingdom, Pineapple Kingdom, Lemon Kingdom, and Grape Kingdom. The J Barrel goes to the Cherry Kingdom, Peach Kingdom, Melon Kingdom, and Durian Kingdom. The B Barrel introduces the player into the Pear Kingdom, Lychee Kingdom, Chili Pepper Kingdom, and Star Fruit Kingdom. Completing all the kingdoms in each barrel allows Donkey Kong access to the next barrel.
Donkey Kong Country and Donkey Kong Land series
The game Donkey Kong Country introduces the generic barrels - and also some other types - as weapons used by Donkey Kong in combat with enemies. They appear frequently in many levels throughout the game. When Donkey Kong picks up a barrel, he lifts it above his head by using his powerful arms. This can be done if the player presses on the SNES controller when the ape hero is next to the barrel. However, Diddy Kong, the second hero, is not as strong to lift the barrel up, and only carries it in front of his body; nevertheless, this is a good technique used to protect himself from hazards. The barrel can then be hurled by releasing the button. Barrels are necessary to destroy tough or well protected enemies, including Zingers and Krushas. The mechanic of a barrel is simple: after it gets picked up and thrown, it will start to roll on the ground until it hits a wall (after this, the barrel will break); every enemy who dares to withstand this mighty weapon will be overthrown and grounded by it. Later in the game, Donkey and Diddy Kong encounter abominable orangutan-looking foes called Manky Kongs, which, much like Donkey Kong in the original Donkey Kong, tosses dangerous barrels at the heroes. These barrels only break when they hit a wall, and oddly enough, when Rambi bumps into a barrel thrown by a Manky Kong, the wooden weapon will not shatter its staves, but instead will simply fall off-screen.
After Donkey Kong Country, throughout the other many adventures of the Kongs, barrels still have the same function as they had in the aforementioned game. Donkey Kong Country 2: Diddy's Kong Quest's barrels do not sport any apparent change, and so they remained in Donkey Kong Country 3: Dixie Kong's Double Trouble!, Donkey Kong Country Returns and its remake, and Donkey Kong Country: Tropical Freeze. Apart from the Donkey Kong Country series, barrels also make appearances in the Donkey Kong Land games, and retain the exact same function. While Donkey Kong Land 2 and Donkey Kong Land 3 are full of barrels, the first Donkey Kong Land features a very small amount of normal barrels, three to be more precise. In this game, barrels are smaller and take the form of wooden kegs.
In Donkey Kong Country 2 and Donkey Kong Country 3, Dixie Kong can lift barrels over her head with her ponytail. Also, exclusively in Donkey Kong Country 3, Kiddy Kong's method of holding barrels is the same as Diddy Kong's.
There are some barrels in the first Donkey Kong Country which do not display gray hoops, but instead greenish ones. When these are thrown, they will roll on the ground just like common barrels, yet they are so fragile they will break when hitting an enemy. Barrels in Donkey Kong Country 3 function the same, although these do not sport any change in appearance from generic barrels.
Super Mario Bros. Special marks the second time barrels are used in the Mario series. In this game, barrels are not called as such, but rather credited as Tarusar. They are introduced in World 3-4 and continue to appear occasionally throughout the game. These obstacles did not change since their latter and first appearance in Donkey Kong; they just roll continously towards the hero, either on castle stairs or on steep mushroomy platforms. Here, barrels apparently spawn and plummet from high areas, and their source is nowhere to be seen. Mario's simple stomps couldn't destroy the wooden hazards, although happily, the game features the overpowered hammer, whose metallic and brutal head stands against anything, not to except barrels. Smashing barrels in this game is a good opportunity for some players to recall how they would smash barrels thrown by a gorilla in the older days.
Barrels are placed throughout dog day deserts and spooky mansions in New Super Mario Bros. Wii, this time as handy items. They can be carried and thrown by the player in order to defeat certain enemies, just like in Donkey Kong Country. However, they can also harm other players if they get hit by one. Broozers sometimes use Barrels as hazards. As seen in World 2-2, barrels can easily break when in contact with a spiked ball, whether they roll into them or stand still.
Barrels appear in Super Mario 3D Land. In the final boss battle with Bowser, there is a point in the battle where Bowser throws barrels at the hero, a reference to the original Donkey Kong arcade game.
Barrels reappear in New Super Mario Bros. U, and act just as in New Super Mario Bros. Wii. In this game they are less common, only appearing in some Ghost Houses with Broozers. Barrels return in New Super Luigi U as rare items, only found in the level Broozers and Barrels. Here, they are usually used by Broozers, but sometimes even by players.
Super Smash Bros. series
Barrels also appear as items in Super Smash Bros. and Super Smash Bros. Melee, where they contain one to four items and can roll along inclines. They also sometimes explode when broken. They return in Super Smash Bros. Brawl, alongside the Crate. This time around, they change appearance depending on the stage in which they appear. For example, it turns into a Present Barrel on the Yoshi's Island stage; though the effect of the Barrel remains unchanged.
Barrels briefly showed up in a microgame from WarioWare, Inc.: Mega Microgame$!, called Donkey Kong. This microgame is based upon 25m, the very first level of Donkey Kong for the arcade. The microgame has Donkey Kong constantly tossing barrels at Jumpman; the character needs to dodge them while he stands still. Likewise, in WarioWare: D.I.Y. Showcase, barrels are featured in an extremely similar microgame, again named Donkey Kong, in which the player must protect Jumpman - who continously walks on the girders and clambers ladders - from the barrels thrown by the simian foe.
Types of barrels
Official profiles and statistics
Super Smash Bros. Melee
Super Smash Bros. Brawl
Names in other languages