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

Mythic Striking

ITEM 20

RARE MAGICAL MYTHIC

Price 70000 gp

Usage etched onto a weapon

Bulk —

This weapon is filled with unmatched destructive power. The weapon deals five weapon damage dice.

Activate—Unstoppable Devastation (concentration)

Trigger You roll the weapon damage dice for a Strike with this weapon and do not like the result

Effect Spend a Mythic Point and reroll your weapon damage dice, taking the higher of the two results.

Craft Requirements Mythic striking 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