Catalytic Entropy

You surround the target with a consuming, entropic aura that slowly grows in power. Make a ranged spell attack roll. On a hit, the target creature takes 1d12 necrotic damage.

On subsequent turns you may use your action to make another ranged spell attack roll in an attempt to expand the aura, causing it to deal more damage. On a hit the damage goes up by 1d12. On a miss, no damage is dealt and the number of dice do not increase, but the spell is maintained. This spell may deal a maximum of 5d12 damage, and when at maximum stacks only requires a bonus action to maintain, without an attack roll.

For each spell slot above 1st level the initial damage increases by 1d12, up to a maximum of 5d12 at 5th level.