A Banana is a popular item found throughout many Nintendo video games, notably the Mario Kart and Donkey Kong Country series, among others. In the Nintendo world, it first appeared in Donkey Kong Jr. for arcades. Mario oftentimes uses it as a weapon, while Yoshi, notably Yellow ones, love this particular fruit. Donkey Kong has a hoard of Bananas in his brand of video games, and oftentimes they'll get stolen by his opponents.
Most recently the item appeared in Super Smash Bros. Brawl in two notable occasions. First and foremost is the fact that it is now an item that can be used while fighting. When tossed on the ground, opponents that run over will slip and fall over.. While it doesn't do any damage, it can be used to gain more time to attack the opponents. The second appearance of bananas is found in the story's adventure mode, where a few of Bowser's minions, consisting of Goombas and Hammer Bros. steal Donkey Kong's banana hoard. Soon after, DK and Diddy go out to retrieve it.
In the Mario Kart series, bananas appear as the Banana Peel item. When dropped, opponents can drive over it and spin out giving the other players the chance to pass them.
In Mother 3, Fassad expresses a taste for bananas and leaves the peels on the ground. Ironically, he fell off of the Thunder Tower when he slipped on one of his own banana peels. The character can also walk over any banana peels they find causing them to fall down, but it does not cause any damage.