From Pathfinder War of Immortals, which isn't enabled.

Mythic Armor Potency

ITEM 20

Price 70000 gp

Usage etched onto armor

Bulk —

This armor is etched with a mythical ward providing unparalleled defense. Increase the armor's item bonus to AC by 4, and the armor can be etched with four property runes.

Activate—Survive Devastation (concentration)

Trigger An enemy critically succeeds against you with a weapon or unarmed Strike

Effect Spend a Mythic Point; if the triggering Strike was made by a mythic creature, it's a normal success instead. If it was made by a non-mythic creature, it's a failure.

Craft Requirements Mythic armor potency runes can only be crafted, etched, or transferred by a mythic character capable of making a Crafting check at mythic proficiency (such as by having the Artisan's Calling).

Pathfinder War of ImmortalsORC