Greninja is a dual Water/Dark-type frog Pokémon, which is themed after ninjas and its species is fittingly known as the "Ninja Pokémon". It was introduced in the Pokémon series within the series' sixth generation, as part of Pokémon X and Y. Greninja is the final evolved form of the starter Pokémon Froakie, who in turn evolves into middle stage Frogadier before evolving into Greninja at level 36. According to the Pokédex and based on its statistics in the Pokémon games, Greninja is extremely fast (in fact, it has the highest raw speed statistic of any Water-type Pokémon or fully evolved starter Pokémon) and relies on this speed in battle and to confound its prey with swift, ninja-like grace before striking with its Water Shuriken move, which is said to be able to shear metal. In exchange, however, it is rather frail due to having and has low defenses.
In the Pokémon games, Greninja has access to numerous unique abilities. In addition to Water Shuriken, which it uses in Super Smash Bros., it is also the only Pokémon able to learn Mat Block, where it flips a tatami mat in front of itself to shield itself and its allies from incoming attacks. In addition to these two unique moves, it has access to a diverse range of offensive and status moves; it can even uniquely take advantage of them with its rare Hidden Ability Protean, which changes its type to match each move it uses and ensures it gets the maximum possible power out of every attack. Its prowess in Pokémon battles courtesy of Protean has led to Greninja to being considered an extremely powerful and useful Pokémon by the competitive Pokémon scene, to the point that is even viewed as an "Uber-tier" Pokémon in the same vein as Mewtwo.
Greninja debuts as a newcomer in Super Smash Bros. 4. It was first revealed in the Super Smash Bros. Direct on April 8, 2014, alongside fellow Pokémon representative Charizard. Fittingly for ninja-inspired character, Greninja is very quick and mobile much like Sheik, yet possesses more consistent KO power overall in comparison to her. It also possesses special moves that can catch opponents off guard, such as Shadow Sneak and Substitute.
Greninja is currently ranked 21st out of 58 on the tier list, placing it in the C tier. Greninja's strengths include very fast overall mobility and great combo potential, most notably with up and down tilts. Water Shuriken also grants it a decent projectile, which not only has fairly good travel distance, but is also capable of being thrown out for a fast attack, or charged up for greater power. Despite these positives, Greninja's flaws include unusually high ending lag in its moveset, especially its smash attacks, Substitute being a weak counterattack due to its low power, and a poor grab game due to its overall sluggishness and unreliability to start combos or even KO. Regardless of these issues, as well as being noticeably nerfed in update 1.0.4, Greninja is still viewed as a viable choice for competitive play, earning it decent results.