setvar 0x8008 0x1 (Why this variable have to be 8008, can't it be 8009 or 800A and so on?)
call 0x81A8CAD
Yup, it can be any stable variable (aside from 0x8004), 0x8008 is just being used to store a value. The reason why it is storing this value and why 0x8004 isn't used can be explained when you look at the script segment which is being called afterwards.
#org 0x1A8CAD
copyvar 0x8004 0x8008 (I know it means "copies value of 0x8004 to 0x8008", but why?)
special2 LASTRESULT 0xFC
copyvar 0x8009 LASTRESULT(Same as above))
return
First off, it the opposite way around, 0x8008 is being copied to 0x8004, meaning that 0x8004 will now have a value of 0x1 thanks to the earlier step (HackMew must have switched this command's imputs in XSE after this script was extracted and expanded upon). In a trading script 0x8004's value indicates which trade will be taking place. Its value has just been changed to 0x1, making it the Poliwhirl/ Jynx trade in Cerulean City.
Several times throughout the script the 0x8008 variable will reappear to copy 0x1 over to 0x8004. This is because there are other specials which also need to use the 0x8004 variable to work - 0x8008 is being used as a simple memory device and will always remind 0x8004 which trade to use (0x1) when it needs to remember it.
0x8009 is serving a different purpose than 0x8008. The special command 0xFC "checks the trade in 0x8004 and buffers the name of the wanted pokemon (0x0) and the given pokemon (0x1)". This means it is storing Poliwhirl's name in [buffer1] and Jynx's name in [buffer2], which can be written in the text part of a script to say the Pokemon names. However, this script is using the special
2 command, which returns a value to the variable given (0x8009) after executing the special. In this case it is storing Poliwhirl's number to be used in the future.
...
call 0x81A8CBD
#org 0x1A8CBD
special 0x9F
waitstate
lock
faceplayer
copyvar 0x800A 0x8004 (I know it means "copies value at 0x800A to 0x8004" but why have to use 0x800A and 0x8004?)
return
...
compare 0x8004 0x6 (Why 8004 is used,but not 8005 or 8006 and so on?)
if 0x4 goto 0x816AA0B
Once again, 0x800A it is storing a value to be used later on in the script since 0x8004 needs to be used in other commands and can't remember it.
0x8004 is being compared to 0x6 as a result of special 0x9F which was used slightly earlier. Special 0x9F brings up your Pokemon party menu and allows you to choose one Pokemon. That Pokemon's position in the party is then saved to 0x8004 and allows you to use other commands with that particular party member in mind. The reason why it is being compared to 0x6 is to make sure that you've chosen a real Pokemon and haven't selected the B/ cancel button. While we generally think in terms of "first party Pokemon, second party Pokemon, third party Pokemon" etc, the ROM starts at "0x0th party Pokemon, 0x1th party Pokemon, 0x2th party Pokemon" etc. This means that the sixth Pokemon in the party will be interpreted to be 0x5. 0x6 and any value beyond that is considered to be an impossible Pokemon/ the cancel button so the script will abort and think you've declined the NPC's trade offer.
...
call 0x1A8CC9
...
#org 0x1A8CC9
copyvar 0x8005 0x800A (I know it means "copies value at 0x8005 to 0x800A" but why have to use 0x8005 and 0x800A?)
special2 LASTRESULT 0xFF
copyvar 0x800B LASTRESULT (I know it means "copies value at 0x800B to LASTRESULT" But what "0x800B" stand for?)
return
...
comparevars2 LASTRESULT 0x8009 (what 8009 stands for?)
if 0x5 goto 0x816AA15
...
It is just copying the result you got above to 0x8005.
Special 0xFF checks the Pokemon stored in 0x8004 and places its number into another variable. 0x8004 is currently still referring to the party Pokemon you chose with special 0x7F so it taking its Pokemon number to be compared later. The script its saying that the Pokemon's number is to be stored in LASTRESULT (0x800D) and then copied over to 0x800B, which is once again holding a value to be checked against/ copied later.
Its a bit strange to see comparevars2 as a command here as it isn't a properly documented command in XSE, I wonder what HackMew was doing. Anyway, it functions in the same way as the comparevars command, oh well.
In this part the script is checking LASTRESULT (0x800D) to 0x8009, which are holding values for the Pokemon number of the party member you selected and Poliwhirl's Pokemon number respectively. It is checking to see if they are the same number and if they are then that means you chose a Poliwhirl from your party and aren't trying to give the old man a dumb Magikarp or another unrelated Pokemon. '0x5' in the last line can be read as 'not equal'.
bufferpokemon 0x0 0x8009(What 8009 stands for?)
0x8009 still holds Poliwhirl's Pokemon number so it is putting Poliwhirl's name into [buffer1].
#org 0x1A8CD9
copyvar 0x8004 0x8008(Why should use 8004 and 8008? or what are they stands for?)
copyvar 0x8005 0x800A(Smae as above)
special 0xFD
special 0xFE
They are just coping over values prior to the actual trading portion of the script (specials 0xFD and 0xFE). 0x8004 is given the trade number to begin (0x1 - Poliwhirl/ Jynx) while 0x8005 is being told which party member is going to be overwritten with Jynx's data.
