They appear in battle over time; the more turns you take with your troops, the more stacks will appear... Sometimes they really bothered me...

They haven't appeared at all for me, and I'm level 32. Questions: 1. What is the red key for if you can get into that area without it? 2. I received the Tome of Summoning, but I can't summon a Phoenix. Is this intentional, or is it a bug? 3. I received the Tome of Light Magic, but there is no resurrection spell. Is this intentional, or is it a bug? 4. Do I need to kill the green player, or can I avoid killing him and still complete the mission? The game crashes very often when loading. But overall, even though I haven't finished the first mission yet, it's a very interesting campaign!