Steam Mephit

A steam mephit on the party's side is a stretch but a fun one. A wizard's bound servant, a fire genasi's distant cousin who owes a favor, or the kettle-spirit a kindly hag promised to install in the party's safehouse all work. Steam mephits are Neutral Evil and rude, but they will hold a contract for as long as the contract is in their interest, and "interest" for a mephit usually means a warm place to sleep and someone to insult.

In combat the mephit is a hazard the party deploys at the enemy. Send it into a cluster of brigands and let Steam Breath drop a 15-foot cone on three of them at once (DC 10 is laughable, but the speed reduction stacks usefully against fleeing or charging targets). Blurred Form keeps the mephit alive for two or three rounds against unprepared opponents who can't see well enough to land hits. When it finally drops, Death Burst goes off at the enemy's feet, and that is the entire pitch. Treat the mephit as a one-use grenade that talks.

Out of combat the mephit is a utility creature. It can heat a kettle, keep a wagon's water-barrel from freezing in winter, hide in a teapot for ambushes, and translate between Aquan and Ignan speakers. Its real value is comic relief. A mephit grumbling about the cleric's hymn-singing or the rogue's morning breath gives the party a non-PC voice at the table for the cost of one binding spell.

When the binding lapses, the mephit leaves on a steam trail with one final insult. Have it call the bard ugly. The bard will laugh and remember it three sessions later.

A steam mephit is a CR 1/4 hazard with a punishment built into its corpse. AC 10 and 17 HP say "easy", but Blurred Form gives the party Disadvantage on every attack roll until the mephit is Incapacitated, and Death Burst hits a 5-foot emanation for 2d4 fire on a DC 10 Dex save when the mephit drops. So melee against a steam mephit is a strange dance: the party misses more than usual, and when they finally connect, the thing detonates. Run them in pods of three to six in places where steam belongs (boilers, hot springs, alchemist labs, geothermal vents).

Open with the cone if it's available. Steam Breath is DC 10 Con, 2d4 fire, 15-foot cone, with a 10-foot speed reduction on a fail until the end of the mephit's next turn. Recharge 6 means it usually fires once and that is it. Pick the moment carefully: a cluster of low-Con casters in a hallway, or a fighter who needs to close the next 10 feet. After the breath, claws are filler. +2 to hit for a flat 1d4 plus 1d4 fire is barely a scratch, but Blurred Form means the party still misses half their swings.

The interesting tactic is positioning the death. A mephit dying in melee splashes 2d4 fire on whoever finished it. A clever mephit (Int 11, fully sentient) angles itself between two PCs as it drops, or backs into the party's healer, so the burst catches the most fragile target. Run the mephit knowing what its corpse will do and play accordingly. The party will figure it out by the second pod and start using ranged attacks, which is the right answer.

Steam mephits speak Aquan and Ignan and they will taunt the party in either language if anyone understands. Two lines of mocking commentary, then they detonate. Write the lines now, while the table is reading the menu, so you don't have to improvise them when the mephit pops.