Plotnick
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From memory, I don't think there's anything here that needs further detail. At the start, you have three strong heroes with decent armies. Each of them moves forward and captures a castle. Then, Faidaen captures the last Necropolis castle and continues north. Godric also moves north and takes the first Haven castle. And Zehir begins clearing the surrounding area and capturing mines. Faidaen takes one castle in the north, then goes through a portal to the second and takes it as well, then moves south and takes the last Haven city. All that remains is to join Raileigh with Shadia, level up, gather troops, and defeat Isabel. Capturing all the castles could be completed on the eighth day if Faidaen and Godric have logistics. But I haven't tried it without logistics.