Blackness

 Choose a tile in which you are planning on casting this spell. The chosen spot erupts with pitch black smoke covering everything in a 15ft. radius. While the spell is active, each creature that starts a turn inside the smoke, including you, must roll a Constitution saving throw, failing which will result in 1d10 necrotic damage. For each turn the creature stays in the amount of damage dices doubles, thus making the damage equal to 2d10 on turn 2, 4d10 on turn 3 etc. up to the damage limit of 10d10. Each time the creature has to repeat the Constitution saving throw.

 When casting this spell using a 4th level spell slot or higher, the radius increases to 30ft.