Dragonfire of the Unrivaled Ancient

This is a 10th level spell.            Casters: 4

You unleash a massive portion of ancient draconic magic channeled from the draconis fundamentum of Klauth, the Unrivaled Ancient and one of the oldest non-dracolich dragons ever known.  Using this power, you exhale a blast of blazing dragonflame in a 95-foot cone, and each creature caught in the blast must make a Dexterity saving throw, taking 32d6 fire damage on a failed save, or half as much on a success.

Once you do this, each caster must succeed on a Wisdom saving throw against a DC of 2 + the main caster's spell save DC or be cursed for 1 day. While cursed, they have disadvantage on attack rolls and saving throws, and have vulnerability to damage dealt by Dragons and their minions.

In ancient time of the world of D&D there were no limits for what magic could do. But then Mystra, the goddess of magic, after having to kill herself to save the weave from Karsus' foolishness, decided that such magic was too powerful, reducing the strength of spells an individual could cast to 9th level. Due to the impossibility for a mortal to have 10th level or higher spell slots, there must be a number of secondary casters, each using a 9th level spell slot, to cast it as shown in the Casters. In addition to the secondary casters there are also the main caster who is the person actually casting the spell. This person chooses the targets of the spell and any other choice that must be made to cast the spell and could actually make a spell target some of the secondary casters even if they did not agree to. If a spell requires concentration its only the primary caster who must maintain concentration. Immediately after casting a 10th level or higher spell, all casters must make a DC (9+spell level) Constitution save or suffer from 1 level of exhaustion (10th or 11th level spell), 2 levels of exhaustion (12th or 13th level spell), 3 levels of exhaustion (14th or 15th level spell), 4 levels of exhaustion (16th level spell), instant death (17th level or higher spell).