Fortress

The style of the Fortress is to never buckle or break beneath the weight of an opponent, however strong. Those who emulate it stand tall, shield in hand, heavily armoured; ready to prove that their defence is the best offense.

Fortified

When you gain this feature at 3rd level, increase your hit point maximum by twice your level.

Whenever you gain a level thereafter, increase your hit point maximum by two.

Defensive Stance

Starting at 3rd level, you learn to maintain a strong, defensive position during combat, and to hold that position with your life.

At the end of your turn, if you did not attempt to attack any other creatures during your turn, you assume a turtled stance. Whilst in this stance, attack rolls against you have disadvantage, and you have advantage on saving throws against effects that would push you or knock you prone. The stance persists until you attempt to attack a creature, at which point the stance is broken.

Unfased

Starting at 7th level, you can levy your adrenaline to shrug off even the heaviest attacks.

As a reaction when you take damage, you can withstand that damage. The damage taken is reduced by four times your fighter level. You can't use this feature again until you take a short or long rest.

Ineffable Endurance

Starting at 10th level, your Second Wind feature is greatly enhanced, allowing you to take up a final stand before defeat.

When you use your Second Wind feature, you instead regain hit points equal to 3d10 + four times your fighter level.

Additionally, when you next take damage after using your Second Wind feature, you have resistance to the damage taken. If you already have resistance to that damage, you instead have immunity to it.

Deflective Stance

Starting at 15th level, you can masterfully deflect incoming attacks whilst defending yourself.

Whilst your Defensive Stance feature is active, when you are targeted by an attack roll, you can use your reaction to increase your Armor Class against the incoming attack by 4. 

Additionally, when you prevent an attack from hitting in this way, you can follow up with a powerful retaliation:

• If the incoming attack was a melee attack, as part of your reaction, you can perform a powerful riposte. Make a melee weapon attack against the creature with advantage: that weapon attack is a critical hit on a roll of 18 or 19.
• If the incoming attack was a ranged attack, you can deflect it back towards it's user. You become the user of that ranged attack, and the original user becomes the target.

You cannot use either of these retaliations again until you finish a short or long rest.

Unbreakable

Starting at 18th level, you have achieved such mastery of the Fortress that you simply cannot be felled in battle.

When you fall to 0 hit points, you do not fall unconscious or make death saving throws.

When you are at 0 hit points, you gain the benefits of your Defensive Stance feature, and can act as normal on your turn. However, you cannot move, attack or cast spells. After spending 3 turns at 0 hit points, you regain a number of hit points equal to your fighter level.

Whenever you take damage whilst in this state, you must make a DC 16 Constitution saving throw or fall unconscious and begin to make death saving throws as normal.