When you cast a spell that has a casting time of an action, you can choose to take 5 Necrotic damage to change the casting time to a Bonus Action for this casting. This damage ignores your Resistance and Immunity, and bypasses your Temporary Hit Points.
You can use this feature a number of times equal to your Charisma modifier (a minimum of once). You regain all expended uses when you finish a Long Rest.