Vengeful

You are determined to deliver retribution to any who strike you down. You gain the following benefits:

• You gain a +1 to your Constitution score, up to a maximum of 20.
• When you take damage that reduces you to 0 hit points, you may use your reaction to make one melee weapon attack as a free action before you fall unconscious. 
• when you make a death saving throw, you regain 1 hit point on a natural roll between 18 and 20. Once you use this benefit, you can’t do so again until you finish a short or long rest. 
• if a creature you can see deals damage to you that reduces you to 0 hit points, you have advantage on your next attack role against that creature. Additionally, the next time that creature sees you move towards it, it must make a Wisdom saving throw against your passive Charisma (Intimidation). On a failure the creature becomes frightened of you for 1 minute. The creature could repeat the saving throw at the end of each of its turns, ending the affect on a success.