Pankratiast

Pankratiast's are unarmed fighters who specialize in grappling, and hand to hand combat. Pankratiatst's (unlike the Monks) ability comes from technical application and not an inner well of power. Pankratiast's love to fight and live to entertain. They can be found in pits and arena's all around anywhere. Whether you're a former athlete trained in hand to hand combat, or a slave used as a pit fighter, You have studied pankration and became well versed at imposing your will on the opposition. 

The Clinch

Beginning when you choose this archetype at 3rd level, your ability to grapple is improved granting you the following abilities when unarmed (you cannot wield a non-unarmed weapon and take advantage of The Clinch):

-When an opponent is grappled by you they are also restrained
-You can initiate and maintain grapple using either acrobatics or athletics

-Reaping Throw: You can use your action surge to perform a Reaping Throw on a grappled opponent. (Athletics vs Acrobatics check) Using a pivot and leverage to sweep their legs from under them and slam them downward.
On success: target takes damage equivalent to an unarmed attack plus and additional hit die. (If normal unarmed attack roll would be 2d8 +stat +prof, the roll for Reaping Throw would be +1d8 making the attack roll 3d8 +stat +prof etc.) and is rendered prone in the space behind you character.
On fail: target manages to roll with the trip and negate all damage but is still rendered prone behind you. (Reaping throw is considered an unarmed attack, and an improvised attack.) 

Dance like a Fairy, Strike Like a Giant

Starting when you take this archetype at 3rd level, you can use technique instead of sheer strength when using unarmed attacks, granting you the following abilities when you are unarmed (you cannot wield non-unarmed weapons and take advantage of class feature):

-Your unarmed fists are considered unarmed melee weapons.

- Unarmed attacks have the Finesse property. 

- Counter Strike: Whenever an opponent lands a melee attack, you may expend an action surge to "roll" with the strike. Use your reaction to make the opponent deal half damage and make a unarmed attack. Timing it just right to take advantage of your opponent's momentum.
On hit: Opponent takes damage equal to an unarmed attack plus an additional hit die and is stunned for one round. (If normal unarmed attack roll would be 2d8 +stat +prof, the roll for Counter Strike would be +1d8 making the attack roll 3d8 +stat +prof etc., CON save ends stun)

ARE YOU NOT ENTERTAINED?!

Starting at 7th level, You are a better athlete than most and like to show it. When you are visible to at least one other intelligent non hostile creature you can add a additional bonus equal to charisma modifier to athletics and acrobatics checks and your long jump/high jump distance gets a bonus increase of additional feet equal to your charisma modifier. Additionally you can grapple as an attack of Opportunity.

Olympian

Starting at 10th level, You can use your reaction to reverse a grapple made by any creature targeting you that you can grapple by winning a grapple check. (Athletics/Acrobatics vs Acrobatics/Acrobatics check)  You deal 2d4 damage to creatures grappled by you at the start of your turn.

Combo Breaker

Starting at 15th level, Your unarmed hands now have the light property and while unarmed, you can attack as though you had Two-Weapon Fighting Style.

Dominance

At 18th level, You become a Pankration Master. Your unarmed attacks do additional damage with each subsequent Unarmed strike. Add strength/dexterity modifier bludgeoning multiplied by each unarmed strike landed to each subsequent unarmed strike. You can grapple as a bonus action. Additionally, a successful grapple is considered an unarmed strike.