Undying Will

You are very determined and have mastered the ability to survive on willpower alone.

When you are reduced to 0 hit points and fail your death saving throws, you can choose to survive. Once this activates, it cannot activate again for the next 48 hours. Additionally, once per long rest, if you are hit by an attack that does leftover damage equal to your total hit points, you do not instantly die unless the attack's leftover damage is at least double your total hit points.