Astram's Marvelous Metal Skin

You touch a willing creature. Until the spell ends, the target’s skin has a smooth, metal-like appearance, and the AC of the Person Affected is raised by +6. The creature affected by spell is vulnerable to lightning damage. While the spell is active the creature can be targeted with spells such as Heat Metal & it's speed is reduced by half.

A creature targeted by the spell cannot be the target of the spells & class features such as Shield that improve their AC excluding wildshape & unarmored defense.