From the Super Mario Wiki
Kaboings are gray and green colored reptilian enemies and members of the Kremling Krew. They look similar to Klomps, but instead of possessing one peg-leg like the latter, Kaboings have two. According to the game's credits, Kaboings belong to the "Kremling Kuthroats" enemy class.
Kaboings are first encountered in Donkey Kong Country 2: Diddy's Kong Quest as common enemies. Due to having two peg-legs, Kaboings are incapable of walking normally and instead bounce and attempt to land on or slam into Diddy or Dixie. A simple bonk on the head is enough to defeat a Kaboing.
In some later levels of the game, light green versions of Kaboings are encountered. These green Kaboings can jump slightly higher and move slightly faster. In Web Woods, green Kaboings wait on higher platforms to jump down and ambush Squitter.
Kaboings also appear in Donkey Kong Country 2's pseudo-sequel, Donkey Kong Land 2, and retain all of their characteristics.
Kaboings appear in the following levels.
Donkey Kong Country 2
Donkey Kong Land 2