Armor of Fate

Whenever you're target of an attack, roll 1d20 in response and add the result to your AC temporary befor the attacker rolls for the hit.
After each attack, the power added to your AC fades and your AC turns back to it's original high.

For each higher Spell Level you use to cast Armor of Fate, add a +2 to the added AC value. (5th Spell Level grants 1d20 additional AC, 6th grants 1d20+2 AC, 7th grants 1d20+4 AC, etc.)