Flappers are underwater, mussel-like foes that appear exclusively in Donkey Kong Land. They commonly dwell the second world, Kremlantis, and return in numerous other underwater areas of the same game.
When attacking, a Flapper claps its mantle together and propel itself upwards. After it reaches a point high enough, it slowly begins to sink. If a Kong touches this enemy while it is moving through the water, he gets injured and passes out. Flappers are often encountered in groups and swim in tight spaces to increase difficulty.
None of the English Donkey Kong Land-related material refer to Flappers as such. However, they are repeatedly described as sea creatures in Volume 74 of Nintendo Power. This descriptor is not used for other aquatic enemies found in the game. The free 24-page booklet of Donkey Kong Land from UK's Nintendo Magazine System instead refers to it as Nemo, which is the name of a separate enemy referred to on the same page as Nautilus.
Names in other languages