Coldfire Blast

You unleash a burst of frozen fire at a target you can see within range, which manifests as a missile of ever-changing ice glowing with a crackling heart. Each creature in a line 5 feet wide and 120 feet long must make a Dexterity saving throw, starting with the creature closest to you. The spell impacts the first creature in the line that fails their saving throw, inflicting [roll]2d8[/roll] cold damage. If all targets succeed, the projectile continues in a straight line until it impacts a surface. Once the projectile impacts something or reaches the end of the line, it detonates in a blast of fire. All objects and creatures within 10 feet of the detonation take [roll]1d8[/roll] fire damage, and unattended flammable objects are ignited.

At Higher Levels: When you cast this spell using a spell slot of 3rd level or higher, either the cold or fire damage (your choice) increases by 1d8 per slot level above 2nd.