Focused strikes

You’ve realized the power of Focused strikes. You gain the following benefits:

Strong Position. If the creature is facing their target, they will gain 2 AC against them.

Limb Strike. Attacks on specified limbs could have possible consequences towards the target of the creature. 

Stance. The creature can break the stance of other creatures (calculated using an equation) which will allow for guaranteed critical hits if broken.

The max stance of a creature is calculated by max HP of the creature multiplied by 2, multiplied by half the armor class, all divided by 4. The stance of the creature will be reduced by the max potential damage of an attack. Once a stance hits zero, the AC is effectively 0, and all attacks against the creature becomes critical. Stance regains after a short or long rest.

For example, if Titana-Boa has a stance of 483. If Miller strikes with his great axe and she blocks it, or Miller doesn't hit above the AC, 0 damage will be dealt to HP, but 13 damage will be dealt to stance. If Miller strikes her 37 times with the same attack, her stance will break, and any attack from there on out will be a critical hit and the AC will not stop attacks.

The mechanic is meant to speed up boss fights and give even lower-level players a good chance of beating any fight.