Delayed Blast Fireball
A glowing bead of yellow light flies from your finger and lingers at a point at the center of the area until you end the spell—either because your concentration is broken or because you choose to end it—and the bead detonates. Each creature in the area takes 12d6 fire damage. If at the end of your turn the bead has not yet detonated, the damage increases by 1d6.
If touched before the spell ends, the creature touching the bead makes a Dexterity saving throw or the bead detonates. On a successful save, the creature can use an action to throw the bead up to 40 feet, moving the area with it. If the bead strikes a creature or solid object, the bead detonates.
The fire spreads around corners, and it damages and ignites any flammable unattended objects in the area.
The damage increases by 1d6 for each slot level above 7th.