Thanks so much for this. I was hoping to save some $$ and only buy Psychic specters. This can be done in some other series (Pokemon, Mega Man Star Force, etc) with existing romhacks/editors but good to know the Yokai editor isn't quite there. Do you know if there are other issues with this approach besides Mystery Way?
There is some way to make it happen, it's just a matter of finding it. I might toy with my files/look at what the current editor is doing whenever i get around to playing these (which could be years from now...), but seems like the safest bet is to just give in and find people to link with or purchase the set. I guess a 3rd option might be a save upload/good samaritan service where a server/someone with access to all 3 versions can trip the linking flags properly given someone's save file, but reverse engineering is probably far less of a hassle for everyone.
Actually, a 4th option would be to simulate a local connection by capturing whatever wireless traffic would occur between two systems and retransmit it over the internet. I wonder if that solution already exists but for a different use case...
Anyway, have fun with Yokai 2
Edit: Got myself curious and sounds like Citra could solve this (option 4). Not quite as good as what i was describing, but if both sides can get to their save files, it should work. Citra's explanation of its multiplayer functionality sounds like it at least.