Martial Archetype - Crusader
Fully clad in shining armor, the Crusader is a wall of steel, the tank of a medieval battlefield. Whether drawing his blade against man or monster, the Crusader strikes true, and always lives to tell the tale. But the strike of a Crusader is not as legendary as their resolve, their seeming immunity to pain and suffering. A Crusader can weather a dozen blows that would fell a lesser man, and continue to march ever onward, to victory.
Beginning when you choose this archetype at 3rd level, you have a pool of delayed damage that allows you to forestall the effects of your injuries. When you take damage, this damage is added to your delayed damage pool, instead of being subtracted from your hit points. At the end of your turn, you take damage equal to the total stored in your delayed damage pool, which then resets to 0.
When you restore hit points, you choose whether it reduces your damage pool, restores your hit points normally, or both (you can split the amount of healing as you wish).
At 3rd level, your delayed damage pool can hold up to 5 points of damage. Any damage beyond that comes off your hit points as normal. The maximum damage your pool holds increases by 5 at 6th (10 points), 9th (15 points), 12th (20 points), 15th (25 points), and 18th (30 points.)
At 3rd level, you gain a bonus to damage on melee attacks equal to your delayed damage pool divided by 5, rounded down.
Beginning at 7th level, you can, as a bonus action on your turn, reduce your delayed damage pool to zero without decreasing your current hit points. After using this ability, you must complete a short or long rest before using it again.
By 7th level, it is exceptionally hard to kill you. You no longer suffer instant death from taking damage exceeding your hit point maximum. In addition, instead of falling unconscious when you are reduced to 0 hit points, you are instead incapacitated and prone. Death and death saving throws otherwise function as normal.
Starting at 10th level, when a creature you can see attacks a target other than you that is within 5 feet of you, you can use your reaction to change the target of that attack to yourself. This attack has advantage against you.
At 15th level, you gain advantage on an Intelligence, Wisdom, or Charisma saving throw. After using this ability, you must complete a short or long rest before using it again.
Additionally, you have advantage on saving throws against being charmed or frightened.
Improved Damage Flush
Beginning at 18th level, you can use Damage Flush a number of times equal to your Constitution modifier. When you do so, you can also end either one disease or one condition afflicting you. The condition can be blinded, deafened, paralyzed, or poisoned. You regain all expended uses when you complete a long rest, or 1 use when you complete a short rest.