I haven't completed any campaigns yet, but I'm playing as Orcs, on map 3. Man, it's such a drag! These Nagas are coming from everywhere – I can barely keep up with defending. I mean, I've gained a ton of experience fighting them, but it's making me feel really unmotivated. I just want to find where those sneaky shamans are hiding. Are they in a dungeon or something?
I didn't find them right away either. I went straight into their dungeon, but I had to retreat because I ran out of strength. The Nagas didn't bother me too much. I had both the Orc and Sandor leveled up. I used Sandor to clear the map, and I stationed the Orc in the main town to guard it. He didn't have an army, though. He has a fast movement speed – he can cover half the map! And I built two teleportation spells in the city. If there's danger, we teleport; if we need to, we move the army from one to the other and teleport the second one to the fortress that the Nagas are attacking. And that's it, suicide attack on the Sanctuary!