Glimmer

Glimmer the Anglerfish is an unplayable Animal Buddy that only appears in one game, Donkey Kong Country 2: Diddy's Kong Quest. In fact, he only appears in one level, Glimmer's Galleon. In this level, Glimmer helps Diddy and Dixie Kong by illuminating a path with the small light attached to his head as the two Kongs swim through a dim sunken pirate ship. Strangely, Glimmer appears on the box art for Donkey Kong Land 2 but doesn't appear in the game itself. In this pseudo-sequel, Glimmer is replaced by light-activating barrels in dim Glimmer’s Galleon.

Glimmer’s role in Donkey Kong Country 2 is very similar to Squawks’ role in the original Donkey Kong Country.

A character similar to Glimmer, conjecturally called Glower appears in Donkey Kong 64.

Glimmer's Fate?
Interestingly, on the box art for Donkey Kong Land 2, Glimmer is shown tailing behind Dixie and Diddy Kong. However, behind Glimmer is a Lockjaw piranha with its mouth wide open, preparing to eat the unsuspecting anglerfish. Perhaps this choice of box art was Rare's subtle way of explaining Glimmer's absence from Donkey Kong Land 2.

It is also possible that Glimmer was crushed or met some other unfortunate fate during the sinking of Crocodile Isle.

Interestingly an anglerfish similar in appearance to Glimmer can be seen in the trailer for the now apparently cancelled game, Donkey Kong Racing. Whether this was Glimmer or just a generic anglerfish is unknown.