Arcane Shield (Feat)

You can convert any spell into a defense.

Prerequisites: Arcane Caster Level 10

Benefit: As an immediate action, you can sacrifice a prepared spell or unused spell slot of 1st level or higher and gain a deflection bonus to AC equal to the level of the spell or spell slot you sacrificed for 1 round. 0-level spells may not be sacrificed in this manner.

Note: This feat lets you use your immediate action at any point prior to damage resolution to attempt to retroactively make a successful attack miss. Obviously, you can also use it before an attack roll.