Baron Kepmak

Legendary Resistance (3/day). If Baron Kepmak fails a saving throw, he can choose to succeed instead. 

Blood Frenzy. Baron Kepmak has advantage on melee attack rolls against any creature that doesn’t have all its hit points.

Limited Amphidiousness. Baron Kepmak can breathe air and water, but he needs to be submerged at least once every four hours to avoid suffocating.

Detective Shark Telepathy. Baron Kepmak can magically command any shark it can see within 120 feet of it using limited telepathy.  Further, granted by the Sekolah Totem, Kepmak can detect any creature that has a swimming speed withing 300 feet of him.

Multiattack. Baron Kepmak makes four attacks when taking the attack action, one with the Sahuagin Trident of Royalty, one with his shortsword, one with his claw, and one with the Rod of Sekolah. 

Sahuagin Royal Trident: Melee Weapon Attack: +9 to hit, reach 10ft., one target.  Hit: 2d8 + 5 piercing damage.  This attack is magical for the sake of overcoming resistance.

Shortsword: Melee Weapon Attack: +9 to hit, reach 5ft., one target.  Hit: 2d6 + 5 slashing damage.

Claw: Melee Unarmed Strike: +9 to hit, reach 5ft., one target.  Hit: 2d4 + 5 slashing damage.

Rod of Sekolah: Magic Weapon Attack: + 6 to hit., range 40/80 ft., one target.  Hit: 2d6 necrotic damage and the target can’t regain hit points until the start of Kepmak’s next turn.  Baron Kepmak shakes the rod and summons a ghostly shark head that takes a bite out of the targeted creature.

Summon Giant Shark.  As an action, Baron Kepmak can conjure up a lesser Maw of Sekolah (Giant Shark) up to 40 ft. away from him in an unoccupied space he can see.  The Giant Shark rolls initiative and is added to the turn order.  If Kepmak is killed the Giant Shark flees.   Kepmak can only have one Giant Shark summoned at a time.

Under Pressure (Rechard 5-6): Baron Kepmak increases the water pressure in a 40ft radius circle, centered on himself.  Baron Kepmak designates any number of creatures to be unaffected by it.  Each affected creature must make a DC 14 Constitution saving throw or take 3d10 cold damage, half on a success.

Opportunity Attack.  Baron Kepmak can make two opportunity attacks per round, but can only use the Claw attack option.

Baron Kepmak can take 3 legendary actions, choosing from the options below.  Only one legendary action option can be used at a time and only at the end of another creature's turn.  Baron Kepmak regains spent legendary actions at the start of his turn.

Detect. Baron Kepmak makes a Wisdom (Perception) check.

Trident Attack.  Baron Kepmak makes an attack with the Sahuagin Royal Trident.

Build Pressure (Costs 3 Actions).  Baron Kepmak makes an Under Pressure Attack.