"Vital Strike (Mythic): Whenever you use Vital Strike, Improved Vital Strike, or Greater Vital Strike, multiply the Strength bonus, magic bonus, and other bonuses that would normally be multiplied on a critical hit by the number of weapon damage dice you roll for that feat.
Extra damage from sources that wouldn’t normally be multiplied on a critical hit isn’t multiplied by this feat."
"Vital Strike: When you use the attack action, you can make one attack at your highest base attack bonus that deals additional damage. Roll the weapon’s damage dice for the attack twice and add the results together before adding bonuses from Strength, weapon abilities (such as flaming), precision-based damage, and other damage bonuses. These extra weapon damage dice are not multiplied on a critical hit, but are added to the total."
The mythic version says that you multiply strength, etc, by the number of weapon damage dice you roll for Vital Strike. If I use a greatsword with a weapon damage of 2d6, that means I roll 4d6 weapon damage for the base vital strike. Which would mean because I rolled 4 weapon damage dice, I multiply the strength, etc, bonuses by 4 for mythic vital strike.
Considering the playtest version only mentions the first version of vital strike and not the improved or greater version, it said to multiply by 2. Which leads me to believe that the developers intended the offical mythic vital strike to multiply by 2, 3 for improved, 4 for greater. But with a greatsword, following the rules, it becomes 4 and 6 and 8. Is this working the way the developers intended or were multiple dice damage weapons not considered when writing the text of the feat?