From the Super Mario Wiki
An Animal Barrel, also known as a Goodie Barrel, is a Barrel with a picture of an Animal Friend painted on the side. Unlike Animal Crates, which contains an Animal Friend, Animal Barrels transform the Kongs into its depicted Animal Friend. These Barrels first appear in Donkey Kong Country 2 and return in Donkey Kong Country 3. They also appear in their handheld counterparts, Donkey Kong Land 2 and III.
If two Kongs enter an Animal Barrel, the resulting Animal Friend has two Hit Points, with an icon of that Animal Friend the bottom-left of the screen, or bottom-right in the Donkey Kong Land titles. This icon indicates the second Hit Point. The Animal Friend loses a Hit Point if injured, and its icon disappears. The Animal Friend loses a life if it loses its second and last Hit Point. It can touch a DK Barrel for another Hit Point, which represents the missing Kong. The Animal Friend transforms back into the Kongs if it crosses the No Animal Sign.
Clapper and Parry are the only two Animal Buddies in the featured games who do not have their own Animal Barrel. In Donkey Kong Land 2, Quawks' and Squawks' Animal Barrels look identical because of the Game Boy's monochrome palette.
While Animal Barrels do not appear in Donkey Kong 64, the Animal Crates behave like them as they transform a Kong into an Animal Buddy. This behavior was also recycled for the Game Boy Color remake of Donkey Kong Country.
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