Regenerative Healing Factor

You have gained through mutative, alchemical, or arcane means the ability to heal quickly from your wounds, making you incredibly difficult to kill. Until the end of the fight, when the player character drops below half of your maximum hit points, your regenerative healing factor kicks in and you gain 1d4 hit points (increased to 1d6 at level 10 and 1d8 at level 17) every round until you reach half of your maximum hit points. You do not gain hit points if your character starts the round with 0 hit points. When your HP is reduced to 0 hit points, you have advantage on death saving throws.