A Green Banana is an item from the Donkey Kong series. It is similar in appearance to a regular Banana, except for the fact that it is green. Despite its coloring, a Green Banana isn't an unripe standard banana.
History
Donkey Kong Series
Donkey Kong Country 3
Green Bananas first appeared in Donkey Kong Country 3: Dixie Kong's Double Trouble!, where they were found in certain Bonus Areas. In these Bonus Areas, the object was for Dixie and Kiddy Kong to collect fifteen of them within a time-limit. If they succeeded, they would be awarded with a Bonus Coin. The catch here was that only one Green Banana would appear at a time, and they would appear in random spots, forcing the Kongs into scrambling to collect them. If the Kongs weren't fast enough, any uncollected Green Bananas would disappear.
Through the use of a code, which could give the Bonus Areas of the game a Christmas theme, the Green Bananas were replaced with presents, which served the same purpose.
Donkey Kong 64
Green Bananas later reappeared in Donkey Kong 64. These bananas are the same as any normal banana, but only Chunky Kong is able to grab them, as it is transparent when another monkey goes to get it.