Otyugh

A friendly otyugh is the disposal arrangement of a dungeon, a guild, or a wizard's tower. The framing that works: a sewer otyugh has been fed by a Waterdeep thieves' guild for a decade and considers their colors safe, a druid maintains a peace with the otyugh in the standing pool below the grove, or the party has bargained with one in a previous session and now it grudgingly tolerates them. It will not travel. It will not fight outside its pit. What it will do is eat what the party brings and trade information for food.

In combat inside its lair, the otyugh defends the entrance. Multiattack with one Bite at +6 (12 piercing, plus the long-rest poison curse) and two Tentacle attacks at +6 with 10 ft. reach grapples whoever the party points at. The party stays out of the pit, the otyugh holds the choke point, and Tentacle Slam at DC 14 Con stuns and bludgeons whoever it dragged in. With 104 HP and AC 14, it can hold against a CR 5 incursion for two or three rounds, which is usually long enough.

Out of combat, the otyugh is a search engine for things people threw away. Telepathy 120 ft. (one-way) lets it answer yes-or-no questions in flat sentences directly into a PC's head. It has eaten everything that fell into this part of the sewer for years, including dropped letters, coin pouches, and the occasional severed finger. Have it remember the seal on the assassin's signet ring the party is hunting. Insight check or persuasion does nothing with the otyugh; only food does.

Decide before the session what the otyugh's price for one favor is. A whole goat is a starting offer.

An otyugh is a sewer-bottom omnivore that hunts by squatting in waste and waiting for something to step within reach. The encounter does not move toward the party; the party walks into it. Set the scene as a flooded chamber, a midden pit, or a flooded crypt with bone meal floating on top, and have the otyugh's tentacles come up out of the muck on the second round of careful movement. Telepathy 120 ft. (one-way, no reply) means the first thing the party hears is a polite voice in their heads saying "feed me, please."

The opening priority is grapples, not damage. Multiattack is one Bite at +6 (12 piercing) and two Tentacle attacks at +6 (12 piercing each, escape DC 13 grapple from one of two tentacles). Aim the tentacles at two different PCs, ideally a melee target and a ranged one. Each tentacle has 10 ft. reach, so the otyugh can grapple two creatures at once at distance and pull the back-row caster into bite range next round. The Bite poisons the target, and a Poisoned target who fails a DC 15 Con save at the next long rest loses 5 from their HP maximum until the Poisoned condition ends. That is the otyugh's signature: the sewer infection that follows the party home.

Tentacle Slam is the round-three play. Once two PCs are grappled, drop the Multiattack and use Tentacle Slam: DC 14 Con save for each grappled creature, 16 average bludgeoning on a fail and Stunned until the start of the otyugh's next turn. Stunned means they auto-fail Strength and Dex saves, drop concentration on anything they were holding, and cannot escape the grapple. Two stunned PCs in a pit with the otyugh is a near-TPK setup for a level 5 party. Use it once and only when both grapples are still live.

Otyughs are smart enough to bargain (Int 6, but they speak Otyugh and project simple thoughts). At Bloodied (52 HP or less), the otyugh stops attacking and broadcasts an offer: leave it the corpse of one party member, or one of the dead enemies the party already killed, and it lets them go. Make the party choose. Otyughs do not chase.