Fencer

The archetypical fencer trades power for accuracy, expertly weaving past blows and striking only when the time is right, using a mix of their dexterity and intelligence. As opposed to most fighters, fencers prefer to sit back and study their opponents, rather than mindlessly leaping into the fray, but they can think on their feet if need be.

Acrobatics Proficiency

When you choose this archetype at 3rd level, you gain proficiency in the Acrobatics skill. If you already have proficiency in Acrobatics, you gain expertise in it instead.

Parry

Starting at 3rd level, your intellect allows you to shield yourself and allies from attacks. If you are wielding a finesse weapon and are not wielding a shield, as a reaction to an attack hitting you or an ally within your melee weapon's reach, you can add your Intelligence modifier plus your proficiency bonus to the target's AC for that attack. You can use this feature a number of times equal to your proficiency modifier, regaining all expended uses of it when you finish a short or long rest.

Reaction Surge

Starting at 7th level, if you are not wearing heavy armor, you can use your bonus action to gain an additional 2 reactions until the start of your next turn. You can use this feature a number of times equal to your Dexterity modifier (a minimum of once), and you regain all expended uses of it when you finish a long rest. The amount of additional reactions increases to 3 at 11th level.

Retaliatory Strike

Starting at 10th level, you learn to take advantage of your enemies' mistakes. If you a wielding a finesse weapon when a creature within your melee weapon's reach misses an attack, you can make an attack of opportunity against them as a reaction. If this attack hits it becomes a critical hit and the target must make a Constitution save, becoming stunned until the end of its next turn on a failure. The DC for this save is equal to 8 + your proficiency modifier + your Intelligence modifier. You can use this feature an amount of times equal to your Intelligence modifier, and regain all expended uses when you finish a short or long rest.

3 Steps Ahead

At level 15, you learn to thoroughly study your enemies. Once per turn, if you use the parry reaction against a creature's attack you may make a contested Intelligence check against that creature. If you win, that creature has disadvantage on all attack rolls against you for 1 minute. This effect ends early if you successfully use this ability again.

Lunge

Starting at 18th level, once per round, whenever another creature you can see ends its turn, you can move up to your movement speed towards that creature as a free action. If you end this movement within your melee weapon's reach of that creature, you can make an opportunity attack against it without using a reaction.