Demon invasion.

To be honest, I don't quite understand what the point of BDP (Battle Damage Prevention) is, or its absence, in this context. I play on Recruit difficulty. For a while, I successfully clear out neutral creatures and level up (in various ways, I've tried everything). But the problem is that after a certain time, a yellow mage with high threat appears and simply defeats me, whether I have BDP or not, whether I'm in a castle or not. It doesn't matter. And if, by some miracle, I survive, another enemy hero immediately appears and finishes me off!!!!!!!!!!!!!!!!