Gekkouga

ゲッコウガ

Greninja is a bipedal, frog-like Pokémon. Its body is primarily dark blue, featuring a yellow chest and abdomen, a white triangular marking above each eye, a light blue four-pointed star on each thigh, and yellow coloration on the lower half of its face. It possesses red eyes with white pupils, and its mouth is concealed behind a large, pink tongue that wraps around its neck and extends outward behind its head. A fin-like extension runs down the center of its head, with similar fins on either side, connected by light blue webbing. Large, white, bubble-like bumps are present on each elbow and knee. Its hind feet have two toes, while its front feet have three; each digit ends in a bulbous tip with yellow webbing.
Greninja can compress water into various weapons to slice through enemies, most commonly in the form of throwing stars capable of splitting metal. It has also been depicted creating water katanas and water kunai in both the animated series and the Super Smash Bros. video game series. As an elusive Pokémon, Greninja moves with swift, rapid, and graceful motions akin to a ninja. It utilizes this speed to confuse and toy with enemies while slicing them with sharp Water Shurikens. It can also form shurikens from mucus excreted from its thighs, creating sharp projectiles able to cut steel cables. As shown in the animated series, Greninja's tongue is extremely long—many times its own height—and strong enough to catch and hold a human. However, it typically keeps its tongue wrapped around its neck like a scarf. This positioning exposes the tongue to air currents, allowing Greninja to detect enemies it otherwise could not see.
Forms
Greninja has two alternate forms: Ash-Greninja and Mega Greninja.
As Ash-Greninja, its appearance changes to more closely resemble Ash Ketchum, specifically in his Pokémon the Series: XY outfit. Its skin becomes a lighter shade of blue, and the yellow on its chest and abdomen is reduced to a much smaller area. The fin-like extension on top of its head and the area between its eyes turn red. The outer part of its side fins turns black, as do its cheeks, which now puff out to resemble tufts of hair with a small, thunderbolt-shaped red streak. It now bears a four-pointed star mark on its back where it creates a large Water Shuriken. Unlike regular Greninja, Ash-Greninja is most commonly seen standing upright and is always male.
Through an occurrence called the Bond Phenomenon, driven by the bonds between people and Pokémon, certain Greninja, such as Ash's Greninja in Pokémon the Series, can tap into a miraculous source of power in battles where they need to break their limits. This has only occurred once in recorded history, several hundred years ago. Ash-Greninja's legs strengthen, greatly increasing its speed; it becomes difficult to see and can defeat opponents in a flash. As seen in the animated series, the large Water Shuriken on its back symbolizes a perfect transformation; before reaching this state, Ash-Greninja is covered in a turbulent veil of water.
Mega Greninja
As Mega Greninja, its body is mostly black, except for its lower legs, upper arms, and hands, which retain their original color, giving the appearance of wearing a ninja outfit. The fins on either side of its head extend outward and turn light blue, resembling shurikens with one edge much longer than the others. The four-pointed star marks on its thighs are replaced by actual water shurikens. Mega Greninja clings upside down to a giant, floating, and continually spinning six-pointed water shuriken created from a gelatinous membrane secreted from its body. The shuriken levitates due to its high spinning speed.
Mega Evolution has significantly enhanced Mega Greninja's reflexes; consequently, it forgoes stealth, showcasing confidence in its capabilities. By intentionally revealing itself, it provokes opponents into attacking, and its sharp reflexes enable it to react accordingly and strike first. The mere sight of Mega Greninja clinging to its giant water shuriken can distract opponents, allowing it to preemptively render them unable to attack by binding them with its long tongue. Once its opponents are immobilized, Mega Greninja charges at them to strike with its massive shuriken.
Evolution
Greninja evolves from Frogadier and is the final form of Froakie.