Young Red Dragon

A young red dragon as ally is a brittle bargain with a creature that considers the party a snack it has agreed not to eat today. The setup is usually a shared enemy (an older dragon, a dragonslayer order, a rival warlord) or a debt the dragon was forced to acknowledge by something it fears more than the party. Make the temporary nature of the alliance loud and clear in the first scene. The dragon will not pretend to like the party.

In a fight on the party's side, run it greedy. Fire Breath catches whatever the party wanted alive, because the dragon does not care about the party's plan. The 30-foot cone will hit the rogue who flanked too eagerly; that's the rogue's problem now. Multiattack with three Rend stacks on the most expensively armored enemy, since the dragon will loot whoever drops first. The party's cleric should not heal the dragon, and the dragon would not accept it; healing implies indebtedness, and a young red is too proud to owe a mortal.

Out of combat the dragon is useless for diplomacy, terrible for stealth (Large, loud, smells like coal smoke), and a constant problem for any town the party tries to enter. It is excellent for transport over open country at Fly 80, if the party is willing to be terrified for the entire flight. Common and Draconic on the language list mean it will negotiate and it will insult, often in the same sentence.

When the favor is done, the dragon leaves with whatever loot it claimed up front and a parting threat about the next time. Anyone who tried to short-pay or claim credit during the operation has just made the wrong enemy.

Have the dragon name its price before the favor, not after. Players hate ambush invoices but they accept up-front contracts.

A young red dragon is the first dragon a mid-tier party fights and the first time they understand what dragons actually are. With no legendary actions, no lair actions, and no spellcasting in this stat block, the threat is raw: 178 HP, AC 18, Fly 80 ft., and a recharge breath weapon that can wipe the back rank.

Open with Fire Breath if it's available. DC 17 Dex save, 30-foot cone, 56 fire on a fail and half on a success. That's enough to drop a wizard on a fail and bloody them on a pass. Recharge 5 to 6 means you'll get it again roughly every other round, so the party should never bunch. After the cone, switch to Multiattack: three Rend at +10 for 13 slashing plus 3 fire each, averaging 39 on a single target. Pick the front-line PC who hits hardest and beat them down before action surge cycles twice.

Run the dragon from the air. Walk speed 40 and Fly 80 mean it should never be on the ground unless it just landed for a Multiattack. Without legendary actions there is no Pounce, so takeoff costs the dragon's full movement; use a three-beat rhythm of land, Multiattack, take off, and the party gets one opportunity attack window per cycle. Stealth +4 and Passive Perception 18 mean the dragon ambushes them, not the other way around. At Bloodied (89 HP) the young red flees if the breath weapon hasn't recharged, climbs to a thousand feet, and waits for the party to leave. It is not yet old enough to die for a hoard. It will be back, and it will know who the cleric was.

Name the dragon and write its name on a notecard. Slide the card across the table the first time the breath weapon recharges. The party should remember whose mountain they're climbing.