Everan's Blooming Darkness

You call forth the spectral flora of the Shadowfell, causing budding datura to swirl in the air around you in a 20-foot-radius sphere. The flowers turn bright light in the same area to dim light.

When a hostile creature you can see makes an attack against a target within the area, you can use your reaction to cause some of the datura to bloom. Magical darkness spreads to fill the area until the end of your next turn. The darkness spreads around corners. A creature with darkvision can’t see through this darkness. Nonmagical light, as well as light created by spells of 4th level or lower, can’t illuminate it.

As a bonus action on your turn, you can dismiss this spell and cause the flowers to wither as they return to the Plane of Shadow. Each creature of your choice that you can see within 20 feet of you must make a Constitution saving throw. On a failed save, a creature takes 4d8 necrotic damage, and it is stunned for 1 minute. On a successful save, a creature takes half as much damage and isn’t stunned. At the end of each of its turns, a stunned creature can make a Constitution saving throw, ending the effect on itself on a success.

At Higher Levels.  When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d8 for each slot above 4th.