Kablooie Duck might be the name of a certain artificially-created anthropomorphic duckling.
Seemingly brought into existence by a malfunctioning Gyro Gearloose invention, Kablooie Duck, whose real name is uncertain, is a clone of Huey, Dewey and Louie Duck, functionally a "fifth triplet" (with Phooey as the fourth). The circumstances surrounding his creation are extremely mysterious, but left the five ducklings with one shadow between them (not attached to any one of them, at that) and Gyro confused to the point of getting his proverbs all wrong when he tried to comment on the confusing situations. By all appearances, things were somehow fixed before long, but how, and what became of Kablooie, is unknown.
Behind the scenes
The mysterious Kablooie Duck appears in the 1982 French game page The Shadow. He did not have a name there. Instead, the fan-made name of Kablooie was developed for him on The Feathery Society on a thread about the character in 2019.
Although the five nephews are not individually named in The Shadow, the one shown in the infobox above can be assumed to be Kablooie via Occam's razor, as the other four all bear colors usually worn by Huey, Dewey, Louie, and Phooey.