Black Devil Armor

A demonic aura exudes from your spellbook and covers you, taking the form of a pitch black winged armor. Targets base AC becomes 14 + its Dexterity modifier. The spell ends if the target dons medium or heavy armor or if you dismiss the spell as an action. The user also gains the ability to fly (Speed fly 60 ft.). In addition, this spell cannot be dismissed by except by the user.

While this spell is active, the user has advantage against all spells and magic based attacks for the duration of this spell. 

This spell is unaffected by "Demon Blade" items.

If used through the "Castless" background:

Anti-Magic Aura The armor captures some of the incoming energy, lessening its effect on you and storing it for your next melee attack. You have resistance to the triggering damage type until the start of your next turn. Also, the first time you hit with a melee attack on your next turn, the target takes an extra 1d6 damage of the triggering type, and the spell ends. This effect will activate upon the user being targeted for attack with a spell.

This spell cannot be activated for 5 minutes after being dismissed.