Body of Frost

When you invoke your Crimson Rite (Rite of the Frozen), you may suffer an additional 1d4 rite damage to transform your skin into a tempered icy shell. You gain resistance to cold damage, add +3 to your AC, and any cold damage you take gives you the Frozen Armor* trait. At the end of your next turn, the frozen armor explodes, revealing your original form and removing these benefits. You may use this feat once per long rest.

*Frozen Armor - You add an additional +3 to your AC. At the end of your next turn, your frozen armor explodes. All creatures within 10 feet of you must make a Dexterity Saving Throw against your Strength Score or take 2d6 cold damage on a failure.

Adapted from Become Blizzard by Kugo