@Riot Writers & Foundation: You have to work out how the supernatural systems of this world function

It's usually one of the indicators to tell well written fantasy apart from generic stuff when the systems behind the magic are explained properly.

I could just look at my bookshelf right now and see tons of authors who did exactly that. It doesn't matter if it's Stroud's Bartimaeus, Paolini's Eragon, Aaronovitch's Rivers of London, Rothfuss' The Name of the Wind, Lukianenko's Nightwatch, Pratchett's Diskworld Novels, or Shinobu Ohtaka's Magi - they all spend a lot of time and effort trying to explain how the supernatural systems work, or how the people interacting with them think they work.

I think the only series that doesn't explain it that I can see right now from my desk is "Harry Potter" - but that's a children's book. A good one, with no doubt, but not exactly an example for high quality fantasy writing.

However, right now in the LoL universe things are just too vague - too vague to even take seriously. If everything is "somehow something magic", then I personally lose interest as the things themselves become meaningless. It becomes impossible to compare the things to another, and of course there is always the danger of the writers doing some stupid ass-pulls with the legitimation of it all being vague anyways.

As for how to do it, I think I have named several good titles above. You could go with the River's of London approach and have an apprentice try to measure magic with scientific means (Piltover Style), you could tell a story from the perspective of a magician or magical being, as it is in Stroud's or Lukianenko's works (Xerath as a candidate maybe? or maybe Ryze?) and how they thing about it, or also possible, you tell a story of a magician getting educated in magic what is something that many of the authors named above do (Ionia would be fitting here, as magic is more common there). And I am sure there are some more good options here.

However, there are a few things you need to clarify before: such as "What is Mana?" - "And what is mana SPECIFICALLY in THIS fantasy world?". Don't just steal concepts that already are part of the fantasy-canon. You are supposed to pick them up and develop them yourself, not just take them as you find them. Another issue would be how Runeterra stands in contact with other realms, such as Celestial, Void, Glade, etc. etc. I'm not even asking for a scientific analysis here, just for some very basic informations that make me see this world as something living and complex and not just another generic setting that I have seen getting poorly executed way too much in literature.

Of course there is also the way of explaining almost nothing and keeping everything mysthical, but the LoL universe lacks the atmosphere required for that. That would be something more found in works of Neil Gaiman, but nothing that would be enough to explain everything going in the world of Runeterra. And to be honest, you are kind late with doing that. When creating a world, establishing the basic rules is one of the things that should be done AS ONE OF THE VERY FIRST THINGS.

To be honest I have almost zero hope that you guys ever get anything done - heck, we still have champions with effectively no lore, YEARS since the retcon. But please, don't add screwing up with something this basic to your list of shortcomings. Runeterra as a world has potential, and I'd hate to see this getting ruined by amateurish work from the writing department.