(Paragon 2): Killed Ashwing (second time). Fought both in an open field and in a castle. It's easier to fight in the castle for one reason: Ashwing heavily casts earth elementals. In the open field, the elementals move freely across the map, but in the castle, they can be contained. The AI behavior patterns that Rince mentioned don't always work, and Ashwing, using Tactics, positioned his infantry troops behind the fence. And only once did the AI actually "surround" its archers and not "jump out" from its wall.
Now I'm considering how to get to the brown tent (everywhere there are brown guards of the passages) or, after giving 2 magic books, go to the city of Blazing Inferno?