Giant Constrictor Snake

A giant constrictor snake on the party's side is a druid's wild shape, a yuan-ti envoy's bound companion, or a swamp witch's pet that the party has bought passage from. Treat it like a guard animal that weighs 800 pounds and has no concept of friend or foe beyond its handler's voice. The handler is the real ally. The snake is the threat the handler points.

In combat, position the snake in water if there's any. The 30 ft. swim speed and the bare 12 AC mean it survives longer with cover than it does in the open. Have it surface under one named enemy, grapple them at escape DC 14, and submerge. The enemy has to deal with the held condition, the bludgeoning, and possibly drowning, while the rest of the encounter continues on the bank. That's the snake's whole contribution. Don't ask it to do anything more complicated, because Intelligence 1 doesn't take orders past "that one."

The exit is a feeding scene. After the fight, the snake eats whatever is still in its coils. Decide before the session if your table wants that on screen. If not, narrate the snake sliding back into the water with the body and let the party hear the splash.

Have the handler sing or whistle the command to strike. Players need a tell to read the encounter shape, and a low note from a hag's lips beats a die roll for tension.

A giant constrictor snake is a 25-foot ambush predator with no stat-block actions, which means you build the encounter, not the rounds. The SRD 5.2 stat block is intentionally bare: AC 12, 60 HP, walk 30, swim 30, Strength 19, Blindsight 10 ft. and a passive Perception of 12. You will be improvising a Bite and a Constrict from the closest reasonable analogue, so flag that to your players up front and stay consistent across the fight.

Run a Bite at +6 to hit for 1d6+4 piercing as the opener and a Constrict on a hit that grapples Huge or smaller targets at escape DC 14, dealing 2d8+4 bludgeoning at the start of each of the snake's turns while a creature is held. That maps to the SRD 5.1 version of this monster and lets the snake do what it's supposed to do: grab one PC, drag them off the path, and squeeze. The 30 ft. swim speed is the gimmick. Stage the encounter in a swamp, a flooded ruin, or a mangrove channel where the snake comes up under a canoe, snatches the rogue, and submerges. The party then has one round to react before the bludgeoning starts.

The snake is Intelligence 1. It does not switch targets, it does not panic, and it does not spread damage. Once it has a meal in coils, that is the only PC it cares about. The rest of the party can hit it freely while it constricts. That is the trade and it makes for a tense fight, because every round the held PC is bleeding and the snake's 60 HP doesn't drop on one good Smite. If a second snake is in the encounter, have them grab two PCs at once. The party then has to decide who to free first, and the answer is a roleplay moment.

Describe the constrictor's body in passes. The party sees five feet of it, then ten, then realize the tail is still in the water. The size is the threat.