Ice Queen's Blessing

When you cast a cantrip or magic spell of any level, you may change its attack type to cold damage. If you make this change, add 1d6 to the spell attack. This die increases to 1d8 at 8th level, 1d10 at 12th, and 1d12 at 16th.

At 20th level your cold damage ignores cold resistance and treats cold immunity as cold resistance.

In addition, when you land a critical hit with a spell attack which has had its damage type changed to cold, the creature becomes restrained and must make a Constitution saving throw equal to your spell save DC or accrue a point of exhaustion. If the creature is resistant to cold damage or is immune to exhaustion then it automatically succeeds on this save.