Unsure if this was used already, as there's quite a large list of fruits. If it's already used, please direct me to it. Thanks.
Japanese Translation: Mokuzai Mokuzai No Mi - The Wood Wood Fruit.
Type: Paramecia
Capabilities: The user of this Devil Fruit is able to turn any part of their body (excluding their head) in to thick wood. They can regenerate lost body parts (except their heads) over a short amount of time, using their powers to grow it back as if it were a tree. They can also alter their limbs in to different shapes and sizes (depending on the physical strength of the user). For example, a Wood Wood Fruit user could turn their arm in to a large wooden stake or a giant mallet. If they've the strength (and momentum, as this would be extremely difficult to perform and recover from quickly in a battle) they can extend and retract their limbs for long ranged attacks, much like the Gomu Gomu No Mi. Wood Wood Fruit users can also propel external wood made from their body (for example, I could turn my arm in to a flat, round surface and fire tiny wooden bullets from it) at the expense of minor fatigue afterwards. The wood made from a user of this Devil Fruit is alive; this means that they are not extremely vulnerable to fire in short exposure, they can wither if conditions call for it (they can also get cold or hot due to traces of water flowing through), and they can bend almost indefinitely, depending on the thickness of the limb.