Tony Tony Chopper's Rumble Ball, Explained

Tony Tony Chopper (トニートニー・チョッパー, Tonī Tonī Choppā), otherwise known as "Cotton Candy Lover" and "Emergency Food" is a fictional character in the manga series One Piece created by Eiichiro Oda. He is the sixth member to join and the doctor of the Straw Hat Pirates. Chopper is frequently featured on official merchandise, serving as a mascot for the series. . The power of the Zoan-type Human-Human Fruit (ヒトヒト の実, Hito Hito no Mi) provides him with the ability to transform into a full-sized reindeer

A Guide to All of Chopper's Transformations in 'One Piece' | The Mary Sue