Cinderglass Reaver

Weapon - Rare - Requires attunement - Varies
A weapon made of dark black and crimson volcanic glass, always warm to the touch. Forged in extreme temperatures from the melting together of volcanic glass with khyber dragonshards.
When attuned, the weapon deals an additional 1d6 fire damage on each strike.
During a short rest, a creature attuned to the item can spend the hour in concentration to reshape the weapon, as the glass remelts and forms into any melee weapon of their choice.