The first final battle was on the third week. My opponent conceded by losing all his birds, while I managed to kill 2 angels, 40 grand creatures, and most of his other units. After that, I gathered everything I could from the three resource nodes, as I had captured the central city first and had a teleportation guild, allowing me to quickly control that city.
With 130 lizards, 33 wyverns, a monarch, and various other units, I attacked his main city. Our stats were roughly equal, but he had fewer troops. Interestingly, I leveled up a Moon spell to level 4 in the first week and then discarded it, but my opponent managed to capture it at level 121. It seems that Moon spell was cursed. Thanks for the game.