Dragon's Bane

You cause the heart to wither which launches a beam of otherworldly magic causing target dragon in range makes a Constitution Saving throw.

On a failed save the Dragon takes 8d12 damage and loses its Draconic Immunities and ability to use its breath weapon for 1 minute.

On a successful save it takes half damage, doesn't lose its immunities or breath weapon, and cannot be affected by the same caster casting this spell again for 24 hours.

When cast using a 9th level or higher slot a legendary resistance cannot be used to bypass a failed saving throw.