Rattly

Rattly the Rattlesnake is an Animal Buddy in the Donkey Kong series who first appeared in Donkey Kong Country 2: Diddy's Kong Quest; despite being an inhabitant of Crocodile Isle, Rattly is allied with the Kong Family and is described as "rebelling" against the reptilian Kremling Krew.

Donkey Kong Country 2: Diddy's Kong Quest
In Donkey Kong Country 2: Diddy's Kong Quest, Rattly is a large green, red-ringed snake who uses his coiled, spring-like body to jump high in the air and reach areas normally inaccessible by the Kongs; he can also defeat enemies that they normally wouldn't be able to, as well as perform a supercharge (which is used for jumping instead of attacking).

Donkey Kong Country 2: Diddy's Kong Quest featured an entire level dedicated to Rattly ("Rattle Battle"), which was also the first level that had the Kongs using an Animal Barrel to physically change into an Animal Buddy.

Levels:
 * Topsail Trouble
 * Rattle Battle
 * Toxic Tower
 * Animal Antics
 * Gusty Glade

Donkey Kong Land 2
In Donkey Kong Land 2, Rattly apparently survives the exploding and sinking of Crocodile Isle (after the events of Donkey Kong Country 2: Diddy's Kong Quest) and returns to aid Diddy and Dixie once more.

Levels:
 * Topsail Trouble
 * Rattle Battle
 * Toxic Tower
 * Animal Antics

Trivia

 * The name "Rattly" is a variation of the word "rattle", which is also what his species is named after.