AstralLein
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Sanya, you're the one who understands spellforce. Look, there's SpellForce 3 Soul Harvest and SpellForce 3 Fallen God, and there's also SpellForce 3 Reforced, which reworks some mechanics from the first two, but it's unclear whether they have the same campaigns or different ones. They're sold separately. In the end, it's unclear whether it's one game or different ones..
As far as I remember, if you install everything correctly on the SpellForce 3 Reforced version, it will work as a launcher for running any of the campaigns or multiplayer with all factions. You install Reforced, and then you download the files from the add-ons. That's roughly how it was done. But that's if you're using Steam and have everything.