Way of the mantis warrior

Long ago, the mantis spirits learned their art of battle, since then a dedicated group have taken in this martial art, reformed it to the physical body. The way of the mantis teaches its student to react, not enact. They focus on taking a deep stance and being ready to strike back at anyone who would attack them. 

Level 3: Mantis stance

You can take a bonus action and action(both are used) to take the mantis stance, you will be in this stance ontil next turn until your next turn. While in the mantis stance your movement becomes 0 and you have advantage on any D20 roll against being moved or teleported. While in the mantis stance, whenever you get attacked by an enemy within melee range you can expend 1 Focus Point and make an unarmed attack or weapon attack against that enemy. Your unarmed attack happens after the enemies attack. If the attack against you missed, you hit with your attack, and if they rolled a 1 on their attack roll that attack crits. You dont expend any action, bonus action or reaction with the unarmed attack.

If you are hit by a attack while in the mantis stance, roll a dexterity saving throw DC 12(+1 for each time you have rolled a dex save while in the mantis stance), if you fail you are no longer in the mantis stance and no longer gain the benefits of being in the mantis stance. If you expended an Focus Point your attack from mantis stance will still happen. On a succes you will keep being in the mantis stance.

Level 6: Stance of a predator

When you are in the mantis stance, your gain bonus AC equal to your dexterity modifier.

When an enemy within you melee range make an attack against a creaute other then you, if you are in your mantis stance you may take an attack action(without exppending a reaction) against that creature, if you are not, you may use a reaction to take an attack action against that creature.

If an enemy attack a creature within 5 feet of you with a ranged attack, you may use your deflect missile reaction as if the attack was made against you.

Level 11: Force of a preying mantis

You have learned from the art of the mantis spirits attacks how to strike your enemies with a precice and strong force.

You no longer need to expend a Focus Point to make an unarmed attack while in your mantis stance. 

When you hit a creature when it isn't your turn, you can expend any amount of Focus Points(minimum of 1) to strike them down. The target must make a Constitution saving throw equal to 10 + your profeciency bonus + the amount of focus points expended. On a failed save, the target has the Prone condition and takes 10 bludgeoning damage. On a successful save, the target takes 10 bludgeoning damage.

Level 17: Predatory strike

You have become a predator ready to always strike at the right moment.

The first attack you make each turn while in the mantis stance, is a critical hit.