Phenomenal

Question: If every natural phenomenon is created by a God or Titan via Avatar, does that mean there are no 'mundane' things and everything is technically magical?

Not at all! Just because something was created by magic doesn't mean it's magical itself. Dirt created by the Earth Creation boon is not magical. It's just dirt. Ditto things made by any other boon or power. Unless something specifically says it creates a magical item - some Artistry boons, for example - it doesn't, and whatever was just created is a perfectly normal, non-magical example of its kind.

So when it comes to solid objects, if it's not a relic, trophy or piece of a magical creature, it's mundane. The vast majority of things that exist in the Scion universe are mundane, which is pretty normal - after all, that's how you know the Legendary things are special. Similarly, living things are always mundane unless they're expressly acknowledged to be Titanspawn, lesser immortals, Scions or some other magical creature. Tigers created by the Paper Tiger boon are just normal tigers; you have to use Nemean Scroll, which specifically says it makes Nemeans, if you want to end up with magic tigers.

If you're thinking more along the lines of the elements, that's where things are a little more tricky. If you can use Fire or Sky boons to attack people with elements and those are magical attacks that are specially treated in Scion's system, aren't all fire and lightning in the entire world also magical? They're not, actually, but there is a little bit more to it. The basic idea is that at some point the god of that element used their Avatar to create a permanent phenomenon in the World, and that phenomenon now runs itself and obeys its own natural laws, becoming a natural and mundane thing rather than a direct use of a power.

We explain it in much more depth in this vlog, starting at about 33 minutes in, so check it out if you'd like to listen to us jibber-jabber about it for a little while.