Sphinx of Valor

A sphinx of valor on the party's side is rare, and the framing that works is sphinx as patron rather than sphinx as ally. The party has answered its riddle, sworn to a cause it considers just, or earned a one-time audience through a quest the sphinx set. The sphinx grants help on its own terms: a single battle, a single act of restoration, or a single piece of true information. It does not travel with the party, and it does not stay past the agreed thing.

In combat, the sphinx is a battlefield clearer. Open with First Roar to Frighten the enemy formation (DC 20 Wisdom, 500-foot Emanation, only enemies are affected since the Roar text reads "each enemy"). Follow on subsequent rounds with Second and Third Roars in sequence. The party should know the order in advance so they can position around it. Two Claw attacks at +12 for 20 each plus the Roar means a single-turn output of roughly 84 damage on the Frighten round, climbing to a wide thunder cone of 44 on the Third Roar round. Save Greater Restoration for the moment a PC takes a level drain or an Exhaustion stack the party cannot remove themselves. Heroes' Feast can be cast before the fight if the sphinx considers the cause worthy of the spell slot.

The sphinx will not lie, even to spare feelings, because Inscrutable cuts both ways and it values truth more than comfort. It will not act against the lawful authority of a higher celestial power, so a quest aimed at a god the sphinx serves is off the table. Once the help is delivered, it leaves with a single line: a blessing, a warning, or a final question the party has to live with answering.

Have the sphinx ask one riddle on arrival and one riddle on departure. Write both before session. The bookend is what the players will remember, more than the damage rolls.

A sphinx of valor is a guardian, not an aggressor. CR 17, AC 17, 199 HP, Truesight 120 ft., Lawful Neutral, Inscrutable (no remote magical observation, Insight at Disadvantage), Legendary Resistance 3 per day or 4 in a lair. The encounter is built around a thing the sphinx is protecting, and the fight starts only when the party fails or refuses the test the sphinx offered. Sell the test first. The sphinx is willing to kill, but it would rather not.

When combat starts, the opener is Roar. Three uses per long rest, sequence-locked, and the order matters. First Roar in round one: 500-foot Emanation, DC 20 Wisdom, Frightened for 1 minute on a fail. Second Roar in round two: DC 20 Wisdom, Paralyzed on a fail with end-of-turn repeats and a one-minute cap. Third Roar in round three: DC 20 Constitution, 44 thunder damage and Prone on a fail, half on a save. The arc is fear, lockdown, then a wave of damage that hits the prone and paralyzed targets at full effect.

Multiattack outside the Roar windows is two Claw attacks at +12 for 20 slashing each plus a Roar use, so the Roar charges deplete fast. Spellcasting at-will Detect Evil and Good plus Thaumaturgy gives information and theatre. Save 1/Day Dispel Magic for the wizard's high-impact concentration spell. Legendary actions are Arcane Prowl (teleport 30 feet and Claw, perfect for peeling off the squishies) and Weight of Years (DC 16 Con, 1 Exhaustion level on a fail, which compounds; spend it on the player already locked down). Burn one Legendary Resistance early on a high-impact spell so the players see the budget is real.

The sphinx will accept a yield. A party that drops weapons after the second Roar and addresses the sphinx in Celestial or Common with the right answer to the original challenge gets a single chance to walk away alive. The sphinx remembers them and the answer they gave. That memory is a campaign hook for two sessions later.