"your knowledge of ff are truly insane SoftReset"

Just FFIX, and not really. Percentage based attacks like Stop and Break, and also things like stealing, I can't even begin to figure out how those work. With attacks you can see everything that's happening so it's just a matter of working backwards from the damage you see. It's basic math, not hard if you have the patience to watch a character attack the same targets for hours at a time :/

"Ultimania and Ultimania Omega are usually the main sources, however, there are some 'other' options out there."

I got everything from good old-fashioned testing. My understanding is that the Ultimania guides are printed only in japanese and are next to impossible to get in North America anyway. I could be wrong though.

"Just to know... every damaging skill in the game (No Mercy, Vivi's magics, Holy, Quina's damaging magic, etc) have a formula, like the Eidolons?"

Everything has a formula, even things like Regen and Life. I haven't figured Regen out though, I know it's 1/16th Max Hp per Regen hit but I can't figure out what determines how many hits a character is entitled to. I know Spirit is the main factor, but not how it works within a formula.