Parry

You are a skillful combatant that can use your defensive prowess to strike lethal blows. When an enemy creature hits you with a melee weapon attack, you can use your reaction to roll 1d4 and add it to your AC until the end of that creatures turn. If the number rolled when added to your AC is lower than that of the attack roll, the enemy creature's attack hits you with bonus damage equal to the 1d4 rolled.

However, If the number rolled when added to your AC is higher than that of the attack roll, the attack misses. You then strike the enemy creature with a melee weapon, automatically hitting and dealing damage as though the strike were a critical hit. 

You must be wielding a shield to use the Parry reaction.