Reef Shark

A reef shark on the party's side is a stretch and the right kind of stretch. A sea-druid wild shape, a sahuagin ranger's bonded companion, a triton's patrol animal, a marid's pet sent to escort the party through a contested reef, or a witch who has put a charm on the local school for one tide cycle. Pick one and let the shark ghost along beside the boat or beneath the swimming PCs.

In combat the shark adds one bite a round (around 1d8+2 piercing at +4) and a 30 ft. swim that is faster than any of the PCs in the water. Its real value is target denial. A circling shark on the party's side keeps enemy sahuagin, merrows, and other reef sharks at distance, since predators read each other's body language and a confident bigger fish in the area changes the calculus. Use this as area control, not damage. The shark's job is to make the enemy think twice about entering the water at all.

Out of combat the shark is a sensor. Blindsight 30 ft. inside a sphere the size of a small room means it notices anything in the water nearby (invisible attackers, hidden currents, the silhouette of something bigger gliding past below). Have it surface and circle once before any genuine threat. The party learns to read the circle as a warning.

The shark will not stay loyal past the bond's expiration. When the wild shape ends, when the druid leaves the coast, when the charm wears off, the shark is a wild animal again. Have its goodbye look exactly like its hello. One fin, gone.

A reef shark is the warning shot before the bigger sharks arrive. CR 1/2, 22 HP, AC 12, swim 30, walk 5, and a stat block with no listed actions. Run the bite as a Strength-based unarmed strike at +4 to hit for 1d8+2 piercing, or borrow the older edition's bite with pack tactics if you want the encounter to bare its teeth. With Blindsight 30 ft. and Perception +2, the shark perceives anything in the water within close range, including invisible swimmers, and that is the actual encounter design lever.

Run reef sharks in groups of three to five. One alone is a speed bump. A school is a problem. Open with the first shark already in melee with whoever fell off the boat, then have two more close from different angles in round one. The shark is unaligned and Int 1, so it does not flank in a clever way. It picks the bleeding target and bites again. Track which PC has taken damage in the water. That is the one the next shark goes for, not because the shark is cruel, but because blood does the targeting.

The 5 ft. walk speed is a hard limit. A shark that beaches itself on a rock or a floating piece of wreckage is no longer a threat. Reward smart positioning. A PC who climbs onto a bobbing crate has effectively ended the encounter for any one shark. The fight then becomes about whoever is still in the water. If three of the four PCs make it to the boat and one is still flailing in the chum, the question is whether the others jump back in for them. That question is what the reef shark encounter is for.

Sharks do not retreat from a kill. They retreat from being hurt. Once a single shark in the school takes serious damage (below half HP) it leaves the area, and the others follow within a round. Don't let the encounter run long. Three rounds and either the party is on the boat or someone is being dragged under.

Describe the dorsal fin once before initiative. One fin, then a second, then a third, and the cleric realizes she counted wrong.