The Ryu Ryu no Mi:Model Tarasque is special Zoan fruit classified as both a mythical and awakend zoan. The Fruit was given to a Former Shichibukai of eras past, who for unknown reasons was given the fruit by the world goverment.
The fruit was said to have look like a blue pineapple, with red lines swirling along it's hexagon patterns. Myth also states, that at random times any of it's ripple patterns would transform in to the apperance of an eye, however, this rumors have only dissmiss as overimagination.
The Ryu Ryu no Mi: Model Tarasque allows the user to indefenetely transform into the beast of legends. It's power is unknown due to it being a well kept secret of the World Goverment. By the very few accounts it is said the user ceases to exist, and in their stead a monster of un-imaginable might and ferocity is born. As an awakend Zoan, it is only specaluted that it also possess the abilty of fast regeneration similar to other awaken zoan found as guards in Impel Down, and as one of the rare mythical zoan type, one can only imagine what one transform with this fruit can do.
As far is known, the goverment has monopolized this fruit since the time of the Void century. For whatever particular reason, it's users have always been pirates, or outlaws who have allied with the goverment at some point in their life, and we're ready to give up their freedom for the fruit's power. It is said those transform with the fruit are taske with guarding an ancient power, and serve as it's ultimate defense if it's whereabouts are ever known (whether it is an ancient weapon or perhaps something else entirely, it is only know by the World Goverment.