The first enemy to attack was a Necropolis (36 Riders, 60 Furies, etc.). I thought I could outsmart him with Nazir, but he had a 50% fire resistance shield, and Nazir didn't do much damage. But Nura defeated him almost without problems in the castle, using two stacks of Mages and other units. Now I have the resources to build Colossi, and I think I will, so I can play with Regeneration. But a Demon is already heading towards me; I hope I have enough time to buy the second upgrade for the Colossi.
Added 23 minutes later
And dead ends don't need to be fixed, especially with two-way portals. There is at least one guaranteed way to escape from any dead end on the map.