You touch a willing creature (you can choose yourself) and they are covered in scales for the duration of the spell. Their AC is 10 + your spellcasting modifier at minimum, and they gain additional effects based on the type of scales chosen. You can choose from one of the following types of scales to grant them, it cannot be changed later during the spell. 

Mirrorscale. Your scales are shiny and reflective like mirrors, reducing all magical damage other than magical bludgeoning, piercing, and slashing damage by the this spell's level. The damage reduced is instead reflected onto each creature within 5 ft of you, causing them to make a constitution saving throw or take the damage.

Stonescale. Your scales are dull and hard as rock, making weapons bounce off of them, causing your AC to increase by half of the spell's level, rounded up. 

Weavescale. Your scales appear plant-like, as if they were made of bark in the shape of scales rather than scales themselves. Your scales knit themselves back together after each attack, reducing all bludgeoning, piercing, and slashing damage by the spell's level.