Houndmaster. Hellhounds that can hear the Houndmaster within 120 feet, are immune to being frightened or charmed.  

Mark of the Houndmaster. Enemies are marked till the start of the Houndmasters next round. Meele attacks from Hellhounds against the marked target deal additional 1d6 piercing damage. Furthermore while the Hellhound chose the marked enemy as their target, they dont provoke opportunity attacks.

Pack Tactics. The Houndmaster has advantage on an attack roll against a creature if at least one of the Houndmasters allies is within 5 feet of the creature and the ally isn't incapacitaded.

Protect me! As long as there is a Hellhound adjacent to an attacking enemy and/or the houndmaster, the hit can be redirected to a hellhound.

Multiattack. The Houndmaster can do 2 chainwhip attacks or one Kill Command

Chainwhip. Melee Weapon Attack: +3 to hit, reach 20 ft., 1 target. Hit: 8 (1d8 + 2) Slashing damage. Marks a target.

Kill Command. The Houndmaster commands a Hellhound , to brutally attack a target.
the target is marked and the next successful Hellhound attack is a critical hit.

Come here! Hellhounds within 80 feet that can hear the Houndmaster, use their reaction to move up to their speed to the Houndmaster.