Double-Edge Strike

You surround yourself in a glowing orange-yellow energy that seems to cause the earth around you to shake. After casting the spell, you must use your action to charge directly at the nearest target that is hostile to you. You make an Unarmed strike against that target with advantage that deals, on a hit, 2d6 + your Strength modifier bludgeoning damage. Also if you hit the target you must succeed on a Constitution saving throw or take 1/3rd (rounded down) of the damage dealt to the target. 

This spell's damage dice increases to 3d6 at 5th level, 4d6 at 9th level, 5d6 at 14th level, and then finally 6d6 at 18th level.