Sahuagin Warrior

A sahuagin warrior on the party's side is the renegade scout who broke from the temple, the captive negotiator the party freed from a coastal hold, or the contracted hunter the seafolk druid lent for a tide-bound mission. Frame the alliance around water access. The sahuagin is the boat the party doesn't have, the swimmer who scouts the wreck, the messenger who can reach a sunken city the rest of the world calls drowned.

In combat, the sahuagin's value is amphibious mobility. Swim 40, walk 30, Aquatic Charge as a bonus action. Use it to flank from the water in any coastal fight, escort a downed PC out of a flooded chamber, or carry messages between the party and a NPC stranded on the wrong side of a river. Two Claws at +3 for 4 slashing each is not impressive, but Blood Frenzy keys off any wounded enemy, so against any sane combat the sahuagin will have advantage on round two onward. Point it at the closest hurt opponent and let it work.

Outside combat the sahuagin is awkward in human company. Limited Amphibiousness means it must submerge once every four hours or start suffocating, so a long overland journey requires water stops. It speaks only Sahuagin, which makes it useless as a translator and dependent on the party for everything beyond pointing. Shark Telepathy lets it call sharks, which is occasionally a logistics win and more often a complication when fishermen complain.

Have the sahuagin refuse one specific order on religious grounds. The taboo it will not break makes it feel like a person, not a hireling.

A sahuagin warrior is a CR 1/2 shark-priest soldier whose entire kit punishes a party that is already bleeding. AC 12, 22 HP, two Claw attacks per Multiattack at +3 for about 4 slashing each. The number to fixate on is Blood Frenzy: the sahuagin has Advantage on attack rolls against any creature that doesn't have all its Hit Points. Rounds two and three are when the math turns, because by then someone in the party has taken a hit, and now both Claws have advantage.

Open the encounter with Aquatic Charge if there's water nearby. The bonus action lets the sahuagin swim its 40 ft. swim speed straight at a target, so a warrior can erupt out of a tide pool, cross 40 ft. of water plus 30 ft. of land, and still get both Claw attacks. Pack of warriors is the standard configuration: four to six of them, half in the water, half on the beach, with the swimmers cycling in and out via Aquatic Charge while the front line keeps pressure. The party fighter pursues into the water and now they have disadvantage on attack rolls and the sahuagin do not.

Damage priority is whoever is bleeding. Once a PC is below maximum HP, every sahuagin within line of sight pivots to that target because Blood Frenzy makes them the highest-EV strike. Healing in the middle of a sahuagin pack is itself a target painted on the cleric. Shark Telepathy adds a wrinkle: any shark within 120 ft. is on the warrior's side. A hunter-shark in nearby water turns the encounter into a CR-3-equivalent ambush.

Sahuagin warriors fight as a unit with morale tied to their leader. If the priestess or baron commanding them dies, surviving warriors retreat into deep water and disappear. Without a leader present, they fight to the last because their religion demands it.