How to get the Wave 4 DLC working in emulators:
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Ryujinx:
1: Install the 16.0.0 prod.keys. NOT 16.0.1 or 16.0.2.
2: Install the 16.0.2 firmware (it will not install if you have the16.0.1 or 16.0.2 keys).
3: Install the Xenoblade 3 v2.0.0 update.
4: Install the Wave 4 DLC (+ Waves 1-3 if not already installed).
It should work now.
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Yuzu:
1: Install the 16.0.0 prod.keys.
2: Install the 16.0.2 firmware.
3: Install the Xenoblade 3 v2.0.0 update.
4: Patch the Wave 4 DLC NSP. (see below for instruction on how)
5: Install the patched Wave 4 DLC (+ Waves 1-3 if not already installed).
6: Run the game, check if the update and DLC are loading.
7 (optional): If the DLC is not loading, patch the 2.0.0 update NSP, and reinstall it. (I needed to do this, but others haven't)
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How to patch the NSP:
1: Get this program:
https://github.com/dezem/SAK/releases
2: Unzip the program.
3: Locate the "Bin" folder, and drop a copy of the 16.0.0 prod.keys into it.
4: Run SAK.exe,
5: Select "Patch NSP".
6: Select "Open NSP", and select the NSP to patch.
7: Select "Patch NSP file". It will take about a minute to finish patching (on SSD, may be slower on an HDD).
8: The patched NSP file will be in the same folder as SAK.exe (the original NSP will be unmodified).
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I've gotten the Wave 4 DLC to run in both Yuzu and Ryujinx like this.