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I'm trying to figure out my damage normal vs critical. I have a+2holy cold iron longsword, I have a base attack bonus of 12, strength mod of +7, mythic power attack, improved critical and vital strike. I believe that works out to 2d8 +21 for a vital power attack. On a critical I get confused I think its 3d8 +65. I've been told a couple of ways to calculate the damage and I just want to make sure I'm doing it right. How badly did I screw this up?

Thank you for your answer in regards to Iomedae, much appreciated.
In a recent game we encountered a headless undead creature. A feint attempt was made and would have succeeded but the gm ruled the creature was not susceptible to the feint. One of the players disagrees with this decision but he went with the decision anyway. I'm a little confused now as to what makes a target feintable. Would you clear this up for me?

Does Imodea have a last name or title she used in her mortal life?