The characters K-O-N-G are a collectible item in every regular level (i.e. not a "K" level or a "B" Boss level) introduced by Donkey Kong Country on the SNES. In the Nintendo Switch game, to unlock the K level of each world you need to have collected all the KONG letters in all its standard levels.

DK’s satisfying, weighty movement paves the way for a challenging, momentum-based platformer that demands more skill and precision than the average Nintendo game. But it stays fun rather than frustrating thanks to incredibly impressive level design that explores every clever idea to the fullest and a ton of hidden collectibles worth tracking down.