Brawler’s Momentum.
When Dervin hits a creature with his Drum Bash, he can immediately move up to 10 feet without provoking opportunity attacks.

Thunder Stomp (1/Turn).
If Dervin moves at least 10 feet straight toward a creature and then hits it with Drum Bash, the target must succeed on a DC 13 Strength saving throw or be knocked prone.

Drum Bash. Melee Weapon Attack: +5 to hit, reach 5 ft., one target.
Hit: 9 (1d10 + 4) bludgeoning damage.
If the target is surprised or stunned, it must make a DC 13 Constitution saving throw or be deafened for 1 minute.

Thundering Beat (Recharge 4–6).
Dervin slams his war drum in a booming pulse. All hostile creatures within 10 feet must make a DC 14 Wisdom saving throw, or be frightened until the end of their next turn. On a success, they are immune to this effect for 24 hours.