Crystal Skin

You encase yourself in a suit of crystalline armor. For the duration, you gain the following benefits:

Crystal Barrier. Your AC increases to 18, provided it's not already higher.

Crystalline Refraction. When you are targeted or damaged by a spell of Level 5 or lower, the caster of that spell must make an ability check using it's spellcasting ability against your spell save DC. On a failure, the spell has no effect on you.

Crystal Wall. Your gain 60 Temporary Hit Points, which last until the spell ends.

Crystalline Brace. You can't be moved against your will in any direction, nor can you be forcefully teleported against your will.

Using a Higher-Level Spell Slot. You gain an additional 20 Temporary Hit Points per level of spell slot above 7.