This has some cool Regicide vibes

Indeed! Inspired by Regicide and Elden Ring. The real test will be to see if the upgrades are well priced or too OP. The mastery is an obvious time sink past the first few unlocks, but gives players something to chase beyond the tons of other abilities.

Also have a PnP expansion ready to go once this is balanced for even more customization .

Any interest in virtual play such as Screentop for cards and Google Drive for the campaign sheet?

Yes, I am considering making a web app for the campaign elements, but hadn't thought of other mediums since I am poor at screentop.gg, TTS, etc. But, it does make sense. I am looking for an illustrator to improve the UI of the sheet as well. Not sure if have each campaign element having it's own page would be better or not? (.e.g., Abilities, Mastery, Feats, and Knowstones each have their own page with illustrations (across 2 double-sided pages instead of 1)).

The campaign sheet is a little tight though I think not overly so; I appreciate that it fits on a single sheet when printed on both sides.

Yeah, I just looked at like Gloomhaven and they just have one spot that you erase and write in the updated gold amount. That seems fragile over time to me.

Now if this was a real product I offered. I would probably just have 12 Knowstone tokens. And the max capacity you can "hold" at any given time are those 12. So if you go over that amount after a run, would have to upgrade some things immediately to avoid wasting excess. But, since this is a PnP it made sense to track lifetime gains, but that would save a ton of space just tracking current value of Knowstones.

FWIW, might consider a counter wheel or the like rather than individual Knowstone tokens. Easier to “save state” between games if you have to put everything away or move locations.