Bronks
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I had some minor issues at the beginning, but after a few attempts, I figured out the trick and completed the mission. You need to capture the first town, develop it as much as possible to have at least some troops, and then either break through the Earth Elementals that block the way to the second town yourself, or wait for the enemy to bring out Phoenixes and kill them, and then take the town. Soon, Gilraen starts running around with a large army. And you, of course, still have a weak army, so you need to run away from him on the map and, at the same time, recruit troops in the two upper towns (Gilraen will take the lower one, and he won't take any other towns from you). And when you have a decent army, you kill Gilraen, and then you can easily kill the Druids.