The object you see before you is best described as an ever-undulating ball of liquid mercury with a red glow deep inside its core. It seethes as your hand gets closer to it.
This item has 6 charges and regains all expended charges at dawn.
As an action you can command the orb of molten metal to transform into any simple or martial weapon of your choice, When you do so it rapidly bubbles and cools before floating into your hand. If it is already transformed you can command it to transform in your hand as a bonus action.
The metal of any weapon it forms into is always made of a dark iron, and the wood of ebony. Large claws are carved into their handles, and a ruby is always embedded into them somewhere. If the weapon it transforms into has the ammunition property each time you attack with it a piece of ammunition made of black iron materializes and then disappears again after it strikes. These weapons always count as magical for overcoming resistances. When not stored in a container the orb floats right beside you just above waist height. If it is not at your side you can summon it to you as an action and as you do so command it to transform.
Flash of Wrath
When you hit a creature with a weapon created from this item you may expend a charge to create a line 100 feet long and 5 feet wide of crackling black energy that includes the target creature. Each creature in the line must make a Dexterity saving throw with a DC equal to 15. A creature takes 8d6 Lightning damage on a failed save, or half as much damage on a successful one.
As an action you may expend 2 charges to shout a command in Infernal. When you do so choose a number of creatures up to your Charisma modifier (minimum 1) within 60 feet to make a Wisdom Saving throw. The DC is equal to 15 plus your Charisma modifier (minimum 15). On a failure they fall prone and spend their next turn groveling.