[BWB2W2] Change Shiny Rate

I think this only works on Windows PC as CT2 is an .exe file. If you can decompress a file some other way though then you might be OK.

So to change the shiny rate on the Gen 5 games, I think the only things you really need are:
1) crystaltile2, you can grab that from here https://romhacking.net/utilities/818/
2) A hex editor e.g. HxD

Then the instructions below apply to all four Gen 5 games (B/W/B2/W2).

Then inside crystaltile2, you want to open the Gen 5 .nds file you want to edit and click on the DS icon at the top to open the file explorer. There should be a file called arm9.bin somewhere - you want then right click that, select "Extract(U)" and save it somewhere.

[FYI, some of the core files inside the ROM have a compression algorithm applied, the method I've said there gives you the uncompressed version of the file. We've got to do that to actually edit the shiny rate!]

Next you want to open this uncompressed arm9.bin in your hex editor.

Then you want to search for the following bytes (just hit Ctrl+F and search it as you would do for text):
082801D201

You should only get one result.

Then that "08" number at the start just needs to be changed for something else!

So right now the value is 8, which is used in the general formula as 8/65536, or 1/8192.

To get the same rates as my Renegade hack you'd want to change it from 08 to 80. The hexadecimal number 80 is equal to the decimal number 128, and 128/65536 is the same as 1/512.

If you wanted the theoretical maximum, you could change the byte for FF, which is 255/65536 or roughly 1/257.

Anyway, to get the 1/512 rate here, we'll change the byte from 08 to 80 and save the file.

Then we go back to crystaltile2 where we originally exported the file, and this time we right-click the arm9.bin and click "Compression". That'll reinsert the now edited arm9.bin file into the ROM and that should give you the new shiny rate.

There's no easy way to test this unfortunately!