Devil Fruits when eaten, grant the eater a special super-human power. The eater has new power but looses the ability to swim.
All Devil Fruits are categorized into three types.
Paramecia type grants its user superhuman power like locking onto target, allows its user to alter body or a part of the body like body of blades, to modify things and environment around him like turning people into objects.
Gomu Gomu no Mi
This fruit gives the user’s body the properties of rubber, making the user a Rubber Human. One Piece’s main protagonist is the owner of the Gomu Gomu no Mi.
Those eat Zoan type gain the ability to transform into an animal. It has several sub-classifications, including: Ancient Zoan, Mythical Zoan, and Artificial Zoan. Ancient Zoan allows eaters to transform into extinct species, Mythical Zoan allows eaters to transform into mythological creatures, while Artificial Zoan allows user to permanently take on an animal characteristic.
Zou Zou no Mi
Zou Zou no Mi allows the user to transform into a mammoth hybrid and full mammoth at will.
Logia-type Devil Fruits allow their users to create, control, and transform themselves into a natural element such as smoke, ice, fire, sand, etc… This type is the rarest of the three.
Moku Moku no Mi
The Moku Moku no Mi’s eater is Smoker. He can create, control, and transform into smoke at will.