Art of Blows

After you make an attack  you can make an unarmed strike as a bonus action 

Your unarmed strike deal 1d4

Ability Score Increase. Increase your Dexterity, Constitutions or Strength score by 1, to a maximum of 20

Flurry of blows. Immediately after you take the Attack action on your turn, you can make two unarmed strikes as a bonus action. You can use this number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.