Relentless

You've grown accustomed to battle, no matter how serious the injuries are, you always manage to carry on due to your iron will and uncanny constitution.

• Your Constitution score increase by 1 and gain advantage on death saving throws.
  
  
• You have 3 Tenacity dice d6 at your disposal. When you roll a death saving throw you can add one or more tenacity dice to the roll potentially turning the fail to a success. You recover all expended dice after a long rest.
  
  
• You get an extra tenacity dice every 4 level after taking that feat.
  
  
• Your Max HP cannot be reduced by any means and you are immune to magical aging.