Vas Inane's Explosive Withering

You draw on the lifeforce of each creature in a 15-foot radius centered on a point you choose within range. A dark, pulsating ball of necrotic energy forms in the center of the radius and erupts violently. Each creature in the area must make a constitution saving throw. Constructs and undead are unaffected. Plants and water elementals make their save with disadvantage. A creature takes 4d12 necrotic damage on a failed save and is thrown 10 feet from the center of the spell, or takes half as much damage on a successful save and is not pushed back.

Nonmagical plants in the area wither and die instantly.

At higher levels: When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d12 for each slot level above 3rd.

At 9th level: When you cast this spell at the 9th level, you may choose one creature to target. Sacrificing half your health to empower your spell, the target must make a CON saving throw, taking necrotic damage equal to 9d12 plus the amount of sacrificed health on a failed save or half as much on a success.