Jsk Wondrous Items:Dragonblood Weapon

Source: Jnome's Secret Knowledge

Dragonblood Weapon

Weapon (Any), Uncommon (Requires Attunement)

A metallic dragon scale of unknown material. When a creature first attunes to this weapon, it takes the shape of any simple weapon or martial weapon that the owner wants. The weapon is a dark, burnished gold that is engraved with draconic runes. The length of the weapon has a deep line that starts where the weapon would be held and ends at the tip or end.
 * Upgrade: When you hit a creature with a weapon attack made by this weapon, you can choose to engulf the weapon with the power of the dragonblood that tempered it, dealing an additional 1d8 damage. The damage matches the type of damage most commonly associated with the dragonblood that tempered it. You can use this ability a number of times equal to your proficiency bonus, and you regain any expended uses when you finish a long rest.