From the Super Mario Wiki
A Mega Snaggles is an enemy that appears in Donkey Kong Country Returns and Donkey Kong Country Returns 3D. It is a large relative of Snaggles, and resembles a great white shark as such. It appears to be gray with a white stomach, and sports sharp teeth.
The Mega Snaggles appears in the Ruins world, in the level Damp Dungeon. It appears at the end of the level, where it guards the Slot Machine Barrel. Unlike its smaller counterparts, there is no possibility to defeat the Mega Snaggles.