Dragon of Darkness Flame

Drawing magic from outside, devilish sources, you summon a dragon made of black flame and it lunges forward into a target you can see. This attack requires two actions, so it will take two turns to summon. The first action will draw forth the energy required to summon the dragon; the second action is the act of summoning it and sending into a target. (Note: this can be done in one turn, but only if you use two actions on that turn) When the dragon is summoned, it leaps forth into one the target, leaving behind a trail of black flame that extinguishes after 1 turn. The line's length is however many feet it is between the caster and the target; the line's width is 5 feet. If someone enters the black flames left behind, they take 1d10 fire damage and 1d4 necrotic damage. The target makes a DEXTERITY saving throw, and on a success, they take 2d6 fire damage and 1d4 necrotic damage. When the target fails its saving throw, the target takes 6d6 fire damage, and 1d6 necrotic damage. At higher levels, this spell gets an additional 1d6 fire damage, and 1d4 necrotic damage. (Yes, this is a YuYu Hakusho reference)