Eldritch Detonation

Make a spell attack against a creature you can see within range, upon hitting, the target takes 1D6 Force Damage and begins to glow an ominous blue colour, shedding dim light in a 5 foot radius for the duration. At the start of that creatures next turn, it errupts with eldritch force, forcing all creatures within ten feet to make a constitution saving throw, taking 1D6 force damage on a failure, and half as much on a pass.

When cast at a higher level, the damage increases by 1D6 for the initial damage and the explosion damage per spell slot level.