From the Super Mario Wiki
The Green Balloon is an item in Donkey Kong Country Returns 3D and Donkey Kong Country: Tropical Freeze. It is identical to an Extra Life Balloon, except, as its name indicates, it is colored green. It can be obtained at Cranky Kong's Shop for three Banana Coins, or at Funky's Fly 'n' Buy for seven Banana Coins.
If Donkey Kong (or Diddy Kong in multiplayer mode) equips a Green Balloon, it brings him back to the stage after falling into a bottomless pit. However, Green Balloons cannot be used in stages which require Donkey Kong and Diddy Kong to keep moving, or when falling into pits is impossible (such as when riding a Minecart or a Rocket Barrel).
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