Original guide by @whisperito on discord, modified by @n123original. This guide assumes you already know how to navigate romfs and use CfgBin Editor. If not, please read the starting guide. Additionally, this guide does not work on B1 and B2.

How to Add Custom Fusions

• First, extract and open combine_config.cfg.bin from data/res/shop.
• Next, duplicate a COMBINE_INFO_* entry, the new entry should appear at the end of the tree.
• Next, configure the parameters
  • IsXYZItem parameters should be 1 if XYZ is an Item, else 0 if it’s a Yo-kai.
  • The ID parameters should be the ItemID if an item, ParamID if a Yo-kai.
• Finally, increment (increase by 1) the ChildCount of the COMBINE_INFO tree that contains the entries.