Black fire blast

You shoot a all black wave of fire from your hand or mouth dealing 5d8 fire damage in a cone shape. If hit take 2d6 fire damage  for 8 turns unless caster defeated 

at higher lvls do higher damage

at lvl 8 you do 10d8 fire damage in a cone shape or in a straight line for twice the range. If hit take 4d6 fire damage for 8 turns

at lvl 15 you do 15d10 fire damage. Can change into a giant supernova. Sets area on fire dealing 8d6 fire damage for 10 turns