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I have another question, about Mastery Books. Do they drop from any or specific (or neither?) monsters? Saw that you could buy them from from an NPC, but those are quite expensive... Everything seems more expensive than they used to be since then last time I played... Mastery Books 20 and 30 increase the SP limit to 20/30, right? Can I use one that is 30 before using a 20? I tried following a few SP guides an they expect me to have all 30 spots for every skill available, iirc. So I have like 7 or 8 SP just hanging atm lol.

I'm afraid those were removed some time ago. Specific mastery books were replaced by Mystery Mastery Books quite a while ago, somewhere pre-Justice/Renegades, and I think those books are replaced too, although I'm not sure. The only option now is either to find old books on mules, which should still work, or buy the Mastery Book 20/30s. Also, you need to use 20 before you can use 30.
I personally don't play in Scania, but maybe somebody who does can help with the books?

One last thing: Nexon replaced the normal AP resets with full AP resets in the Cash Shop some time ago. While I don't know how expensive they are, they might be a decent option because I seriously doubt there will be anymore full AP resets coming this long after Tempest.