Demon invasion.

I thought it was really tough before. The Orcs were useless... In the 5th scenario (snow), each guard unit consists of at least 2-3 stacks of various creatures, or even a full army. Heh.
I cleared the mines and that's it... I need to break through to the second castle and combine the armies - there's nothing to do around the first one (the guards are strong) - almost everyone gives a beating. Although, if you wait a week...
P.S. The mentor's guard is awesome!