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1. Regarding hero specialization, this is perhaps one of the least explored topics to date. Attempts to figure out what's what have been made repeatedly, but, unfortunately, they haven't been fully completed. Because this can only be determined through lengthy testing, and this was done before, but no clear system in the frequency of skill improvement has been observed. This applies not only to skeletons but to all units.
2. Magic. There is an inaccuracy in the terminology in the reference guide. "Magic Power" should be replaced with "Knowledge," and everything will fall into place...
3. The number of shots for the ballista has already been corrected :) It's just that the new version of the reference guide hasn't been released yet... :) Although it's long overdue.
Thank you for all the comments.