Greninja is a Water/Dark-type Pokémon that was first introduced in Generation VI of the Pokémon franchise. It is the final evolution of Froakie, one of the three starter Pokémon in the Kalos region. Greninja is known for its speed, agility, and its unique ability, Protean, which allows it to change its type to match the type of the move it is using.

In the Pokémon games, Greninja has been a popular choice for competitive battling due to its high speed and versatile movepool. It also gained significant popularity due to its appearance in the Pokémon anime, where the character Ash's Greninja had a special form known as Ash-Greninja that was exclusive to the anime.

Overall, Greninja has become a beloved Pokémon among fans of the series and continues to be a popular choice in both casual and competitive play.