Horned Devil

A horned devil on the party's side is a contract, not a friendship. The party signed something, or they have leverage on its superior, or a warlock at the table negotiated it as a one-shot summon for a specific target. Spell out the contract before any combat. The devil agrees to fight one named enemy, for one named duration, in exchange for one named price. The price is always future leverage. The party should feel the bill accruing every minute the devil is on the field.

In combat, run the devil mercenary. Hurl Flame from 150 feet picks off the enemy archers and casters first, since those are the targets a Hell-soldier prioritizes by training. Multiattack with Searing Fork on the heavy melee enemy, and Infernal Tail on whichever enemy looks like the leader, since a leader who is bleeding 3d6 a turn cannot give orders. The devil will not heal the party or provide cover, and it ignores anything outside the contract, including a bard going down ten feet away.

Magic Resistance and the +8 Cha save mean the enemy spellcaster's Banishment will probably fail, which the party should appreciate. Diabolical Restoration is the contract's escape hatch on the devil's side: if it dies in service, it reforms in the Nine Hells with the contract noted, and someone in Dis will be along to renegotiate.

When the contracted job is done, the devil leaves immediately, in sulfurous smoke, mid-sentence if it wants. Anyone who tries to extend the deal verbally has just opened a second negotiation, and the price will not be friendly.

Have the devil sign the contract in the party's blood, then hand them a copy. Players treat their character sheet differently when there is paperwork attached.

A horned devil is a Hell-rank line officer with the lungs of a siege engine. It enters the encounter from above, 60 feet of fly speed, and it has a 150-foot range on Hurl Flame so the party hears it before they see it. Set the encounter in a space with at least 30 feet of vertical room. A horned devil that has to walk is a horned devil that is doing it wrong.

Open with Hurl Flame from outside engagement range. Three attacks at +8 for 26 fire each works out to 78 average per round on the back line, which is enough to drop most squishies in a single turn before any party member has cast a spell. Once the party closes, switch to Multiattack with Searing Fork at +10 for 24 average (15 piercing plus 9 fire), and replace one attack per turn with Infernal Tail. Tail is the play that wins the fight: DC 17 Dex save against an infernal wound that loses the target 3d6 HP at the start of every turn for a minute or until a heal lands. Stack three wounds on three PCs and the cleric is now spending all their slots stanching, not damaging. The Medicine DC to clear a wound without magic is also 17, and most parties cannot reliably hit that.

Magic Resistance plus saves of +10 Str, +7 Dex, +5 Con, +1 Int, +7 Wis, +8 Cha means most disabling spells slide off. Banishment is the threat to plan against. Save an Infernal Tail use for the wizard the moment they posture to cast it. The devil is immune to Fire and Poison and resistant to Cold, so the cleric's prepared elemental damage was the wrong list. Reward the player who pivots to radiant or force.

Horned devils do not last-stand for nothing. They are line officers and they answer to a pit fiend. Once Bloodied with no obvious win in sight, the devil flies straight up out of melee, hurls flame from 150 feet for one more round, and disappears into smoke. Diabolical Restoration means it reforms in the Nine Hells, and the party has just made an enemy who knows their faces. The next contract on their heads has a discount.

Have the devil speak first via telepathy 120 ft. before the fight starts. One sentence in Infernal, translated by whoever in the party speaks it. Players remember being addressed by name across an empty room.