Ranger - "Higher Vampire" [5th Campaign, 5th Mission]

Regarding point 3 – completing the prophet's quest (by returning the dwarven artifacts in exchange for 5 phoenixes) directly affects Nikolai's survivability; otherwise, he will constantly respawn near one of the ground-based Necropolises.
And if the dragons shown are not killed, their number will start to increase by 600+ per day from a certain point, and then nothing will help the elves (this is what the video is about).