Need help and advice for HGSS ROM hack.

[SkyZ33]

Hi guys, very new here and I kinda need a little help. long story short with some friends we decided to work on a group project ROM hack of SoulSilver we are using the EU version of the game. Currently stuck at something particular. So we decided our version will have 3 difficulty modes that will have various effects on the game, one of them being the EXP gained after battles. and we've been working on this for a few days now. So we want to add an EXP multiplier, but we can't narrow down the location of the original EXP code. So if anyone can help if they have done something like this before that will be super helpful.