In Generation VII, Greninja with the AbilityBattle Bond can transform into a special form known as Ash-Greninja after defeating an opponent during battle. Greninja with Battle Bond is treated as a distinct form in the games' code.
In Pokémon Scarlet and Violet, Battle Bond's effect was altered to only increase Greninja's stats when defeating an opponent, with the transformation into Ash-Greninja no longer being present.
Greninja is a bipedal, frog-like Pokémon. It is mostly dark blue with a yellow chest, a white triangular marking over each eye, a light blue four-pointed star on each thigh, and yellow on the lower half of its face. It has red eyes with white pupils and its mouth is hidden behind a large, pink tongue that wraps around its neck and extends outward behind its head. Running down the middle of its head is a fin-like extension, and there is a similar fin on each side of its head. Light blue webbing connects its head fins. There is a large, white bubble-like bump on each elbow and knee. Its back feet have two toes, while its front feet have three toes. Each digit has a bulbous tip and yellow webbing.
Greninja moves with the speed and grace of a ninja. It uses swift movements to confuse its enemies while it slices them up with weapons made of compressed water, most commonly in the form of throwing stars. These throwing stars are sharp enough to split metal. In Generation VI, Mat Block was its signature move. In Generation IX, Water Shuriken is its signature move.
But Ash-Greninja can create more than just Water Shurikens
Greninja has an alternate form: Ash-Greninja
Through a process called the Bond Phenomenon, certain Greninja, such as Ash's Greninja in the anime, can change into an alternate form called Ash-Greninja. In this form, Greninja's skin turns a lighter shade of blue, while its face gains red stripes and its cheeks and side fins turn black, changing shape to resemble Ash's hair. Its legs are stronger in this form, and it gains the ability to form large Water Shurikens on its back. Ash-Greninja is always male.
Greninja, the Ninja Pokémon, and the final evolved form of Froakie. Greninja can compress water into sharp-edged throwing stars. With the grace of a ninja, it slips in and out of sight to attack from the shadows.
Five Greninja appeared in Detective Pikachu. They were genetically modified and put in chambers. They were later used to chase after Harry Goodman, and also Tim and Lucy when they broke into Howard's facility.
In the Generation VII games, a Greninja with the Ability Battle Bond will transform into Ash-Greninja after it directly causes an opponent to faint without ending the battle. It will remain in this form until either it faints or the battle ends; in the former case, this prevents it from changing back into Ash-Greninja for the remainder of the battle. Ash-Greninja has different base stats than regular Greninja, with increased Attack, Special Attack, and Speed. Additionally, the moveWater Shuriken will be more powerful, having 20 power instead of 15, and will always hit 3 times, instead of varying between 2-5 hits. Ash-Greninja has been removed from the core series in Pokémon Scarlet and Violet due to Battle Bond having its effect changed.
Internally, standard Greninja with Battle Bond are considered to be a separate form to Greninja with Torrent or Protean. These Greninja are always male, cannot breed, and, like Special Pokémon, are banned from the Battle Spot. A Greninja with Battle Bond can be transferred to Pokémon Sun and Moon from the Special Demo Version. This is the only way to obtain it, so it is no longer obtainable for players who did not download the demo before the discontinuation of the 3DS Nintendo eShop on March 27, 2023.
Greninja's overall appearance is based on a frog, and it may have been inspired by horned frogs from the generaMegophrys and Ceratophrys due to the spiked protrusions above its eyes. Its color scheme and body shape is similar to that of the splendid leaf frog. The bubble-like protrusions on its body may be based on a toad's parotoid glands, possibly referencing the traditional myth of toads causing warts, though they may also be remnants of Froakie and Frogadier's frubbles.
As its species name implies, Greninja is also based on a ninja. Japanese culture associates frogs and toads with ninjas based on the folk story The Tale of the Gallant Jiraiya (Japanese: 児雷也豪傑物語 Jiraiya Gōketsu Monogatari), about a ninja who can shapeshift into a large toad. Greninja and its pre-evolutions may also draw inspiration from the thief or rogue character class in role-playing games, which are generally ranged combatants that often rely on speed and stealth, focusing more on dodging attacks rather than withstanding damage.