I have found that the HP increases mythic offers and save issues with high level (20th+10th tier) need some major fixes. i think that for the HP increase in particular more is the answer. I'm suggesting 10 X tier in Hp for each tier (for a total at 10th of 550). This means at low tier get a nice increase to lasting power even versus mythic foes and at high tier mythics are simply hard to one shot (even among their peers). For saves I think an addition to the mythic save ability would help, my idea is an increase to all saves based on 1/4 the mythic characters level (+1 being minimum). I feel this increase isnt big enough to negate spellcasters bonuses from level progression but does add enough to make enough difference that rolls are still required. Finally i feel Mythic versions of Great Fortitude, Iron Will, and Lightning Reflexes should allow rerolls against mythic sources as well. If anyone has anything to add or wants to point out anything I missed please let me know.