Spellfire Storm

You conjure a pillar of spellfire in a 20-foot-radius, 20-foot-high Cylinder centered on a point within range. The area of the Cylinder is Bright Light, and each creature in it when it appears makes a Constitution saving throw, taking 4d10 Radiant damage on a failed save or half as much damage on a successful one. A creature also makes this save when it enters the spell's area for the first time on a turn or ends its turn there. A creature makes this save only once per turn.

In addition, whenever a creature in the Cylinder casts a spell, that creature makes a Constitution saving throw. On a failed save, the spell dissipates with no effect, and the action, Bonus Action, or Reaction used to cast it is wasted. If that spell was cast with a spell slot, the slot isn't expended.

When you cast this spell, you can designate creatures to be unaffected by it.

Casting as a Circle Spell. In addition to the spell's usual components, you must provide a special component (a blue star sapphire worth 25,000+ GP), which the spell consumes. The spell's range increases to 1 mile, and it no longer requires Concentration. When the spell is cast, each secondary caster must expend a level 3+ spell slot; otherwise, the spell fails.

Using a Higher-Level Spell Slot. The damage increases by 1d10 for every spell slot level above 4.

The number of secondary casters determines the spell's area of effect and duration, as shown in the table below. The spell ends early if any caster who participated in this casting contributes to another casting of Spellfire Storm as a Circle spell.