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For those who like to play it safe.
Trying to overwhelm the yellow heroes is pointless because they constantly reappear, like cockroaches, from two locations. Even if you kill one, they immediately reappear; it's always Ibba, Helmar, and Erling. You are only allowed to hire two of them. Therefore, after capturing the second Dwarven town and placing a second Ashu there, Zehir can go north to look for the red tent. More precisely, first, he needs to gather academic troops to break through the neutral creatures and guards along the way. Zehir can go down, but Wulfsten cannot go up, so in the end, when you transfer some of the artifacts to him, you can also take all the troops from the two Dwarven towns, and give Wulf all the academic troops, because the yellow heroes don't have the same troops as Rolf, and even Zehir. For example, during my second playthrough of this mission, Zehir couldn't defeat Rolf with academic troops, so I exchanged them for a guaranteed victory. Alternatively, instead of placing the second Ashu in the northern Dwarven town, you could place it in the Academy, which might lead to a different outcome, but I'll try that next time. And that's how I passed the mission, but in the end, Wulfsten didn't gain a single level during this mission, and it's hard to say if that will be enough for the end. (Zehir is level 28, Wulf is level 25)