Caustic Stinger

A phantasmal scorpion stinger composed of acidic energy appears from somewhere on your back. You may make a melee or ranged spell attack so long as the target is within 15 ft. of you, but the type of attack must be stated before the roll. On a hit, the target takes 2d10 Piercing damage, and must succeed on a Constitution saving throw or take additional Acid damage equal to half of the initial damage. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d10 for each slot level above 3rd.