Taxon's Creeping Cold

You throw a lapis lazuli gemstone onto a surface within range. The gemstone shatters and spreads out in a 35ft cube. The affected area becomes covered in a creeping cold, becoming difficult terrain, impeding those who pass through, and extinguishing all non-magical flames within.

The first time a creature enters the zone, or starts it's turn within the affected area, it must make a dexterity saving throw against the caster's spell save dc or be frozen over by the cold, dealing 4d4 cold damage, and applying the Restrained condition to the creature. A creature killed by this initial damage is frozen solid until thawed by magical means. A creature restrained by the ice can use its action to make a Strength check against your spell save DC. On a success, it frees itself.

The affected area is considered magical cold, and cannot be heated by non-magical flame. Targets inside of the zone cannot be ignited or set on fire

At Higher Levels: When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d4 for each slot level above 4th.