The unfortunate part of finding this is that there's too many 29 7F, 29 80, 29 3F, 29 40, 29 FF 3F, 29 FF BF numbers to maintain that controls the signed values.
Once Passed value 00 80(the normal negative signed numbers), the calculations check for Miss!, effected characters, and ailment conditions all in the same damage calculation.
Weird and for now the FF 3F is the max That I could get it too. FF 3F is +16,383; FF 7F is -16,383. Pass 00 80 is Miss! and other calculations.
I've tried Lots of combinations Like changing 29 40 to 29 60, 29 80 to 29 C0 or 29 60, and the like to the 3F's and 7F's. and the displayed number shows half or if the like of negative number and sometimes would kill everything on screen.
Also the Numeral Generator for the HP doesn't care about signed value limits, but it does in the Field Main Menu which shows up as 0 pass 42367 for some reason. I think the rom or I made the change for some set value to be at A7 somewhere. So the Value Presented is 5F EA in Battle, and Max in FMM is 0F A7.
