As a living machine, you are able to learn fast and adapt in combat.
As such you gain the following benefits (per creature and weapon eg. Goblin#1 with a spear,)

After begin hit 3 times by a creature with the same weapon you can increase your AC by your dex modifier (minimum 1) from that weapon's hit bonus
if you get hit another 3 times the creature has disadvantage on the attack roll that weapon.

After hitting a creature with a weapon 3 times in a row, you gain advantage on attacks against that creature with that weapon.

If you crit a creature with a weapon, you can now crit on a 19 or higher, with that same weapon and creature.
if you crit again the roll needed to crit goes down by 1 maxing out at 17.

 optional (for groups of creatures of the same races and weapons double the number of times you get hit before obtaining the benefits )