Coldfire Blast

The freezing cold of the desert night compares favorably to the burning sunlight.
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 2d8 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 1d8 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.