Greninja is a large, bipedal, frog-like Pokémon. Its body and legs are dark blue, with single large white bubbles on its legs and arms and white spots over its eyes. On the sides of each of its upper thighs is a light blue, four-pointed star, which resembles a shuriken. Its back feet have two toes, while its front feet have three toes. Its feet are webbed, and it has a yellow chest and a yellow-and-blue face. It has eyes with white sclera, red irises, and white pupils. A large, projecting dark blue stripe runs down the middle of its head, with projecting light blue stripes in between its large, yellow ears. Its mouth is hidden behind a large, pink tongue that wraps around Greninja's neck and extends outward behind its head.
Greninja moves with the speed and grace of a ninja, using swift movements to confuse its enemies while it slices them up with throwing stars made of compressed water; these throwing stars are sharp enough to split metal.
Greninja shares its category with Ninjask. They are both known as the Ninja Pokémon.
Greninja won first place in the Japanese Pokémon general election 720 (Japanese: ポケモン総選挙720) poll to decide what Pokémon would be distributed at showings of Volcanion and the Mechanical Marvel in Japan.