Thunderous Unarmed Attack

(You can only take this feat if you have the unarmed attack feature)                                                                                                                                        When you hit an unarmed attack on an enemy you can make the target make a strength saving roll (DC = 8 + proficiency bonus + strength modifier), or suffer one of two of the following effects:     

The creature is pushed 5 ft. times your strength modifier, the number of ft. you push the enemy is reduced by 5 ft. for each size the enemy is bigger than you, and the opposite happens if the creature is smaller than you. for example: if you have a strength score of 18 and your size is medium and you use this feature on a huge creature, instead of 20 ft. you will push the creature 10 ft.

All creatures in range of 5 ft. of the target takes 5 thunder damage.