What Exactly is a "Nonmythic Source" ?

[Merkatz]

I'm seeing this in a couple of places, but here is one example:

Iron Will (Mythic)
Your will is incorruptible.
Prerequisite: Iron Will, 3rd mythic tier.
Benefit: Whenever you roll a Will saving throw against a spell, spell-like ability, or special ability from a nonmythic source, you may roll twice and take the best result.

Does anything with a Mythic Tier or Mythic Rank count as a mythic source? EG if a Mythic Wizard casts a normal Dominate Person, would Iron Will (Mythic) apply?

Or would this just apply to those specific Mythic Spells or regular spells that have been modified in some way with Mythic Power?

I am curious, because if everything a Mythic character does counts as Mythic, how do some of these feats/abilities work in higher Myth/Level games? If I am playing as a 15 level character with 7 Myth Tiers, how many things am I fighting with absolutely no Myth levels? If the answer to that question is "almost none" then would things like Iron Will (Mythic) become completely useless?

[Jason Bulmahn]

Yup... Anything with a mythic rank or mythic tier counts as mythic. The spell or effect does not need to be modified to count as mythic, so long as the caster is mythic.

I envision that mythic characters will not be fighting other mythic foes on a constant basis. There would be plenty of fights against nonmythic opponents.

Jason Bulmahn
Lead Designer
Paizo Publishing

[Merkatz]

Okay, sounds good.

Thanks Jason.

[Roberta Yang]

The ambiguity I can see regarding mythic damage, etc is the question of when something is considered from a mythic source.

Mythic character shoots an arrow at you? It's from a mythic source.
Mythic character flies directly above you and drops a boulder on your head? It's pretty clearly from a mythic source.
Mythic character places a boulder at the top of a hill and pushes it so it rolls down the hill, hitting you? Presumably from a mythic source?
Mythic character places a boulder in the ceiling that falls on your head when you step on a pressure place? ...no longer from a mythic source?
What if I come across and read something that a mythic character previously cast Explosive Runes on?
What if instead the mythic character casts Explosive Runes on something, hands it to me, and says "Here, read this"?

I suppose rulings like these are why GM's exist, but a couple more guidelines would be nice.