Death's Bounty

You call the deathly chill of winter to wither your foe.  When that creature succumbs, an explosion of spring's vitality is left in its wake.  Choose one creature within range and make a ranged spell attack against that creature.  If that creature's current hit points are less than half its maximum hit points, you make this attack with advantage.  The target takes 3d8 cold damage and 3d8 necrotic damage on a hit, or half damage on a miss.  

Hit or miss, the target becomes marked by the Primal Spirit of Death and Renewal.  If the target drops to 0 hit points while it is marked in this way, it dies immediately in an explosion of vital energy.  This explosion is a sphere with a radius of 10ft centered on the place where the target died.  Any ground within the sphere becomes overgrown with grasping vines and flowering plants.  Allies who start their turn within the sphere gain temporary hit points equal to your spellcasting ability modifier.  Enemies who start their turn within the sphere must make a Stregnth saving throw, becoming restrained on a failed save.  A creature restrained in this way may use its action to repeat this saving throw, freeing itself on a success.  

Maintaining the mark of the Primal Spirit requires concentration, and if your concentration is broken before the target dies, the explosion of vital energy does not occur.  However once the target dies under the mark of the Primal Spirit concentration is no longer required to maintain the sphere of vines and flowers, as the plants instead sustain themselves by feeding on the soul of the recently deceased.  The plants remain capable of granting temporary hit points and restraining enemies for 1 minute before becoming lush non-magical greenery.  

The plants created by this effect can be damaged and thus destroyed.  Any 5ft cube of these plants has AC equal to your spell save DC, and 1 hit point.  A creature restrained within such a cube by these plants when the plants are attacked takes full damage from any attack or effect that hits the plants.  

Undead and constructs can not be subject to the mark of the Primal Spirit, tho they can be restrained by the plants and vines.  

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

Additionally, when you cast this spell using a spell slot of 6th level or higher, the radius of the explosion increases to 15ft, and allies who start their turn within the area gain temporary hit points equal to twice you spellcasting ability modifier.  When you use a spell slot of 8th level or higher, the radius increases to 20ft, and allies gain temporary hit points equal to three times your spellcasting ability modifier.