How to change an in-game trade in HGSS for rom-hacking purposes.

[Goukizeme]

Hello, I'm working on a rom hack, and one of the things I needed to learn for said rom hack was how to edit an in-game trade to be completely different than the original trade. I couldn't find many resources on how to do this, and had to troubleshoot today how to achieve this. So, I'm posting my findings for future people having the same problem. Enjoy.

 

For this example, I will be using the violet city trade. Normally, the NPC requests a bellsprout for an onix named Rocky. There are a few different things needed to do to change every aspect of the trade. I accounted for the following things: The trainer dialogue where he mentions the pokemon by name, the requested pokemon (bellsprout), the given pokemon (onix), the nickname of the given pokemon, and the held item of the given pokemon.

 

1. Lets start with the trainer dialogue. This step and the nickname are fairly easy. For my own needs, I wanted to change the requested pokemon to Sunkern, and the given pokemon to a Pichu named Sparky. For this step I used the tool “DS Pokemon Rom Editor Reloaded” better known as DSPRE. Once you have DSPRE downloaded, open it and load the rom you want to edit. Head over to the Text Editor tab, and in the Search bar type in the name of a pokemon from said trade. This will most likely yield you a few results, but look for the dialogue the NPC says before/after trading. In this case, my NPC says “I collect Pokemon. Do you have BELLSPROUT? Want to trade it for my ONIX?” “Yay! I got myself BELLSPROUT! Thanks!” “Huh? That’s not BELLSPROUT. What a letdown…” “You don’t want to trade? Aww…” and lastly “Hi, hows my old ONIX doing?”. Now while some of these lines don’t need to be edited, click the window that they’re contained in and edit whatever parts you want. My personal changes were just changing every uses of “BELLSPROUT” to “SUNKERN” and every usage of “ONIX” to “PICHU”. Once you are done with the changes, go ahead save the rom and enjoy!

2. On a similar beat as the last step, the Nickname of the given pokemon is also fairly easy to modify, and in a similar fashion too. Simply download and boot up the “DS Pokemon Rom Editor Reloaded” (DSPRE), use it to load your rom, and navigate yourself over to the Text Editor tab. There, type in the searchbar the nickname of the given pokemon. In this scenario the nickname is “Rocky”. Edit the name to be whatever you’d like, which in my scenario I changed it to Sparky to fit Pichu more accurately. Simply save the change and export the rom.

3. To change the pokemon in a trade we have to do some hex editing. Hex editing is achieved usually with a tool like Crystaltile2, but we need another tool to get a file from the rom. So, download NitroExplorer2b, and load your rom into it. From here I followed a tutorial with pictures from this link which puts you into a 2 post rabbit hole on how to do this. Follow those tutorials and when you’re done with those, come back to this one.

4. Now that you’re done learning how to better hex edit your desired given pokemon, we have to figure out how to edit the requested pokemon, and the item of the given pokemon. For these, I improvised. Using a list of every gen 4 item hex decimals, and a list of every pokemon in gen 4’s hex decimals (both of which can be acquired through the aforementioned link), I checked to see if Bellsprout’s hex was in the same code as the given pokemon, which luckily it was. Using the list of pokemon hex decimals, find and replace the requested pokemons hex with the hex of whatever pokemon you’d like, for me I put Sunkern. As for the item, simply find and replace the hex of whatever item is already being held by the trade pokemon (in my case a persim berry). If the pokemon isn’t holding an item and you want to give it one, I bid you good luck. Personally, I don’t understand hex decimals, and I haven’t run into this issue yet, so I do not know how to solve it. If anyone does, please link it in this thread.

 

Hope this was of some use.