Haymaker

You can use your action to make a Haymaker, a single heavy attack using the full potential of your offensive abilities. When you perform a Haymaker, make a single melee attack against a creature within your reach. This attack is made at advantage.

On hit, multiply the damage dice and applicable modifiers by the amount of attacks you could make that turn. If a spell or effect allows you to use additional actions, bonus actions and other resources to make additional attacks, you can use these resources and additional actions to increase the damage of your Haymaker. If you successfully hit the creature, you may also push it 10 ft. away for each attack used. If a creature pushed this way hit an object or other creature that interrupts its movement, it takes an additional 1d6 bludgeoning damage for every 10ft remaining to be pushed and so does the object or creature that interrupted its movement. 

Hit or miss, this attack drains much of your stamina to perform. Immediately after performing a Haymaker, make a consitution saving throw with DC = 10 + the amount of attacks used. On a failure you gain 1 level of exhaustion, your speed is reduced to 0, you can’t take reactions and you can only take an action or a bonus action, not both, until the end of your next turn. Success or not, you cannot perform another Haymaker until the end of your next turn.