When you make a death saving throw and roll a 19-20 on the d20, you immediately regain 1d6 hit points.

Blood Frenzy

When an attack scores a critical hit against a living creature within 15 feet of you, you can use your reaction to roll and expend 1 hit dice.

Until the end of your next turn, you gain advantage on attack rolls against that creature and your critical hit range is expanded to 19-20.

The first time you hit the creature with an attack you deal additional weapon damage equal to the hit dice roll + your constitution modifier.

You cannot use this feature again until you complete a short or long rest.