I apologize ahead of time for the long post and all the reading.
First of all i should give the back story for my campaign. the back story lies in my friends campaign that i helped him make. The campaign took place centuries after most current campaigns after a militaristic warlike nation has dominated all of the inner seas and even more. Well the story should have probably been mythic but my friend wasn't comfortable running a mythic campaign so we didn't make it mythic. The reason it should have been mythic was because the lore behind my character was he was something i created called the guardian. Essentially in ages long past two minor deities ended up going to war against each other Van'dalygon the Dragon of the Black Flame, and Zargoth The Demon of Death. They went to a war that threatened to destroy the world so the gods chose a warrior, a champion of sorts. Zargoth killed many out of hate and anger toward the living and ended up angering Van because he was a god of survival patron of the dragons so when Zargoth started killing dragons he flew into a rage. The original guardian who took up arms and defeated the rampaging gods and imprisoned them in to separate sets of swords. Zargoth swore revenge upon the world claiming to return one day. However Van realizing how much life had been destroyed due to his rage asked the guardian to take up his weapons against evil in order to prevent any atrocity of this magnitude from ever happening again. So the first guardian was born as the guardian he is immortal as long as he fights for good. A guardian is chosen based on his qualities of character and once another Possible guardian is born he is tested and if he takes up the mantle then the current guardian becomes mortal and trains the new guardian before living out a mortal life. Our story takes place with the current Guardian Garrett Church (my character in the campaign) who is trying to stop the main villain Vance who was the best friend of the former Guardian who killed his best friend after falling under the influence of the two Demon swords years ago. so he kills his best friend then goes to infiltrate and take over the Imperium (evil nation) using them to dominate the world and trying to start a war to engulf the world as the legend says Zargoth will be reborn when the world is engulfed in chaos "as brother kills brother and the ground soaks with blood the hate and chaos shall free the demon lord from his prison to bring the end of days and eternal darkness." so needless to say good triumphs and Garrett and his companions who gain some of Garrett's powers from Van and are now known as guardians defeat Vance and seal him away into the swords along with Zargoth and end the war allowing the Alliance (good nation united under the guardians) to reign.
My campaign takes place 10 years later after the Imperium is almost exterminated. However all is not well in the world Garrett and Claire (the main two guardians) have left and haven't been seen for ten years the Ranger guardian is also missing Edward the cleric of the group goes on to lead the Alliance in the chaos. Well Vance was a master strategist and foresaw his possible defeat and so he made a contingency plan he had a mighty military general named Mathius make a deal with Zargoth that in 10 years should the Imperium remain or not he would "ascend" essentially becoming a very powerful Balor lord slightly weaker than a demon lord. His goal is to release Zargoth and Vance in order to continue their work. The new heroes are pulled into this war in order to uncover Mathius plans (at this point they have no idea what his ascension means all they know is he made a deal with Zargoth for power and has risen from the grave) and to stop him. They encounter the guardians along the way (including the missing ones) and see all these fantastical things the guardians do and meeting creatures of legend trying to stop the rebirth of a demon lord.
My issue is i don't know whether or not to do a mythic campaign or if i do when i should implement it. I plan for them to encounter Mathius and have him change into the Balor lord around 15-17 level and they will be forced to flee as he will be far to powerful that would be a good time for them to need the mythic powers as at this point it is believed Garrett, the only one who could possibly stop Mathius, is dead. however they will find him alive but with no memory and i figured when they restore his memory he would make them guardians as well. The guardians themselves are definitely in the mythic realm so it wouldn't be out of the question. However i have never been in a mythic campaign let alone run one so i don't know if it is worth it or not. Garrett's class alone is a high fantasy class i made myself.
So in short i wanted advice from people who have done mythic campaigns on whether or not it is worth introducing the mythic system and if so should i do it as soon as possible or would i be able to introduce it at level 15-17 which would work story wise.
