Which Pokémon has the signature ability 'Battle Bond'?

Greninja is the Pokémon associated with the signature ability Battle Bond. The ability links Greninja’s strength and appearance to its relationship with its Trainer, most famously Ash’s Greninja in the Pokémon anime.

In the games, Battle Bond was introduced with Greninja in Pokémon Sun and Moon. When a Greninja with Battle Bond causes an opposing Pokémon to faint, it can transform into Ash-Greninja, a stronger form visually inspired by Ash Ketchum. The form changes Greninja’s appearance and improves its offensive power, making the ability unlike an ordinary stat-boosting effect.

Ash-Greninja originated in the anime before appearing as a special game-related form. Ash and Greninja developed an unusually close partnership in the Kalos series, eventually synchronizing their movements during battle. That storyline helped make Battle Bond one of Greninja’s defining traits, even though most Greninja encountered in the games do not have it.

Battle Bond should not be confused with Protean, another ability associated with Greninja. Protean changes the user’s type to match its move, while Battle Bond is tied to defeating an opponent and triggering the Ash-Greninja transformation.