Curse of impaling bone

The bones of your foe begin to rapidly grow in spikey patches on the creature's skeleton, slowly impaling the target from the inside out. Targeting a creature in range spikes of their own bones begin to grow and pierce the flesh, growing larger at time progresses. When you first target a creature with this spell it deals 1d8 pricing damage as the initial spikes grow. on consecutive rounds the damage dies increase by 1d8 per round that the spell is maintained up to 3d8 per round. After being affected by the initial damage of this spell a creature makes a constitution saving throw at the start of each its turns to delay the progression of the spikes for one round on a successful save. 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the potential damage cap increases by 1d8 for each slot level above 1st. (ex. casting a spell at 2nd level will increase the damage cap to 4d8 per round).