Flame Blade

Source flame blade

The blade's damage increases to 2d6 points of fire damage + 1 point per caster level (maximum +20). The blade threatens a critical hit on a natural 18–20 as if it were an actual scimitar.

Augmented (3rd): If you expend two uses of mythic power, the blade threatens a critical hit on a natural 15–20, and bypasses hardness, fire resistance, and fire immunity.