I downloaded the megamod 8v but how do i add it to my steam mods?
You need to drop the 3 Megamod1 2 3 .pkm files into the "windata" mod folder found at : Steam/SteamApps/common/baished/windata
Then in-game you'll have to make sure they're in the right order in your modlist and activate all 3. (I recommend disabling everything else, MM is huge enough to not need extra stuff, at least until you're used to it)
Once you've confirmed the changes and let the game do its automatic reload, take the time to entirely exit Banished and relaunch it before you start playing a new time. It's the only way to make sure the changes to your modlist got correctly handled and will spare you some later crashes.
