One Piece Devil Fruit Lamp - "Hito Hito No Mi, Human Human Fruit"
 
A cool fruit design, but probably the most useless power for a human ever is Tony Chopper's Hito Hito No Mi model human.
Or in Usopp's words - no one would want this fruit.
So what does this wonderful looking devil fruit do to its user? It makes him a human being. Of course, this seems completely useless at first, and of course, one could speculate whether it could transform a human user into different forms, as in Chopper's case. But in the hands of an animal this Akuma No Mi naturally results in exactly the same effect as a Zoan animal fruit in the hands of a human.
So Chopper, who was actually a reindeer, can now take the form of a human relatively anthropromorphically. Whether they make him small or large, he knows how to take advantage of it. And with the help of his specially created Rumble Ball, he can even expand these forms and turn into a giant fighting monster.