Martial Arts Initiate

You have training in unarmed fighting and martial arts. You gain the following benefits:

• When you take the Attack action on your turn, you can use a bonus action to make an unarmed melee attack. You may make this attack even if you hands are not free to do so, headbutting, kicking, or even biting your enemy. This does not change the damage type. 
• When you make unarmed melee attacks, you may use either strength or dexterity for this attack, the damage die for this attack is a d4, and it deals bludgeoning damage. If you already have a feature that gives you a die for your unarmed strikes, you may instead increase the damage die by 1 size (e.g. d4 becomes a d6, d6 becomes a d8.) 
• You become proficient in acrobatics, if you are not already. You may add twice your proficiency bonus when making acrobatics checks. This does not stack if you already have an ability allowing to add your proficiency more than once, such as expertise.