Fafnir

Fafnir is a treasure-killer transformed into a dragon by possession, betrayal, and the curse of hoarded gold. He lies upon wealth that no longer enriches anyone, breathing poison across the approaches and interpreting every living visitor as another claimant. The dragon's vulnerable underside and the cursed hoard are both parts of the encounter; taking the gold without resolving its history repeats the transformation in another form.

Poisoned Earth: creatures in a 60 ft cone make a Tough save. On a failure, a creature takes 5d10 poison damage and becomes weary; success halves the damage and prevents the weariness. Hoard-Sweep: Fafnir scatters cursed treasure across a 30 ft cone. Creatures there make Quick saves or take 3d10 bludgeoning damage; anyone carrying away a coin also suffers the curse described below. A successful save avoids the bludgeoning damage.

Pit Beneath the Dragon: an attacker concealed in a trench beneath Fafnir ignores DR on one strike against the underside. Carrying away cursed gold imposes -2 Mind until it is relinquished or purified.