Black Flash

When you cast this spell, you may use a bonus action to do so. During your next turn, roll 1d20 with your dexterity modifier. If the roll is above 13, you may deal an extra d8 of thunder damage with your action if you land a hit. On your next turn, make another d20 roll. The roll decreases by one each turn until it fails. This is called the zone.

Damage increases by 1d4 per player level.