As an action you are able to Channel the Abyss from where your powers come. Every creature you see within 15 feet of you(allies included) has to roll a Wisdom saving throw (DC equal to 8 + your proficiency bonus + your Charisma modifier) if they fail they take 2d4 necrotic damage and you are healed for half this amount. If they succeed they only take half damage and you heal none. 

You may only use this once per Long Rest

You get two uses at Level 6 per long rest and 3 uses at level 18