In its infant state which is known as "Froakie", this pokemon does not look very flattering. The species used to be a massive pest in the Kalos region after a foreigner brought a Froakie from a distant land; with population numbers of Froakie and Frogadier rising to their millions. At this time no one had seen a greninja before nor had an individual had the chance to fully evolve. Froakie were very difficult to catch due to their swift speeds and nimble physiques the species brought havoc on the ecosystem consuming all the regions bug species and affecting the aviary populations.
The Kalos government out a swift stop to it and within months of the species introduction, they started eliminating the population using a popular starter pokemon for trainers, Chesnaught who's Grass and fighting type capabilities perfectly combated and crushed the Froakie and frogadier.
Soon the numbers dwindled to non-existent and none remained in the wild....only well know Pokemon Professor Augustine
Sycamore had some specimens in captivity for study. Rumours spread that the pokemon no longer existed in the region that it originated from and the specimen that Professor Sycamore had truly were the last of their kind. Suddenly public interest in Froakie and Frogadier exploded with people coming from around Kalos to see this rare pokemon. Eventually Professor Sycamore was able to evolve a Frogadier in front of on lookers. When people gazed upon the Mature form of Froakie they were astonished...in it's place stood and swift, agile and graceful pokemon which they dubbed Greninja for its ninja-like discretion and its dark typing. Trainers began to petition for Froakies to be the new Kalos water starter as they were tired of using Kanto's stand in Squirtle and wanted something new, unique and exciting.
In modern times professor Sycamore has successfully been able to stably breed enough froakies to provide new trainers with their starter pokemon. Many people are willing to bear with the unorthodox pre-evolutions to finally get their "ninja-frog" Greninja.
In battle Greninja's speed is rarely matched by it's opponents, it can use its long tongue which is so long it has to be wrapped around it's neck to latch onto opponents and ledges and pull itself towards them.Usually it does not require this as it's jumping prowess is only matched (and slightly outdone) by blaziken. Star Like patches on it's lower legs secrete water from its bloodstream this is combined with a secreted chemical agent unique to froakie which gives the water non-newtonian fluid like properties allowing it to harden when thrown as "water shurikens"....They harden and are particularly sharp upon impact and are a common tactic used to defeat foolish trainers who try use a Delphox against it.
If greninja's mystery was not enough as it is....rumour has it that the pokemon has a hidden ability that can change it's type at will due to a mutation that allows rapid manufacture of polypeptides to completely alter it's cellular structure. Tests on certain greninja with the mutant gene have shown for example, before using the battle move "Toxic" greninja's cells alter themselves to mime those of a typical poison types' giving the poison more potency before the strike and making Greninja itself immune to poisoning until its cellular structure is altered again.
They are quite easily defeated by the Kalos grass starter Chesnaught chenks-r.deviantart.com/art/CH…
. If they do not have this unique ability.
based on Arvalis's work arvalis.deviantart.com/