Black Whip of Avitus

You create a black, whip-like tendril covered in acidic sludge that lashes out at your command toward a creature in range. Make a melee spell attack against the target. If the attack hits a creature made completely out of metal or rock, it deals full damage.

The spell's damage increases by 1d6 when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6).