Brazth's draining tendrils

Four black tendrils come out of of your back and float in the air. The tendrils can reach out in a 10 ft sphere around you. When ever an enemy enters that space or starts its turn there, if one of the tendrils are free, it you can make and attack roll against them. On a hit, they deal 2d4 necrotic damage and make a strength save. if the creature is a medium size or smaller, the the tendril grapples them and suspends them 5 ft in the air, if the creature is larger the tendril wraps around their arm or leg. while the creature is in contact with the tendril, they take 1d6 necrotic damage. as an action, they can attempt to break free of move away from the tendril, if so they must make a strength saving throw. on your turn,  you can cause all the tendrils to drain the life from your enemies or for them to attack, each does something different. 

drain:as a bonus action each enemy that is in contact with the tendrils must make a constitution save or take 1d6 necrotic damage and you gain half of that in temporary hit points

attack: as an action, all tendrils that are free launch at enemies, if any hit they take 2d4 necrotic and make a strength saving throw, else the things above play out

at higher levels more tentacles are created when cast