Eldritch Fire

Eight green balls of fire gather around your finger before converging into a green tinted fireball that streaks towards a point in range. Choose a target in range and make a ranged spell attack.

On a hit, the target takes 1d8 necrotic damage, and on each of your turns for the duration, you can use your action to deal 1d8 necrotic damage to the target automatically. The spell ends if you use your action to do anything else. The spell also ends if the target is ever outside the spell's range or if it has total cover from you.
Whenever the target that was hit makes an attack roll or a saving throw before the spell ends, the target must roll a d4 and subtract the number rolled from the attack roll or saving throw.

Hit or miss, the fireblast then expands. The target and each creature within 20 feet of the point of ignition must succeed on a Dexterity saving throw or take 3d6 fire and 3d6 necrotic damage or half as much on a successful one.

The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6/1d8 for each slot level above 3rd.