I think the higher rank Myth spells are a little awkward to use. These are just my ideas on how to buff the Rank 8, 9 and 10 Myth spells while still respecting the Spell Audits rules and school identity.
Medusa: 750 damage. Stun for 2 Rounds IF thetarget had no shield before the hit.
Celestial Calendar: 930-980 damage. -70% shield on Minion Only.
Also I think it's worth noting that playing Myth has noticeably 0 advantages over playing Fire. Myth is worse than Fire in every meaningful way. What's up with that? Sorry for complaining but am I missing something?