Demon invasion.

so, the further fate of Sigrif will remain a mystery to me*:D

Too bad, but what can you do.
In this map, there are 2 formidable heroes - Hangwul and Wulfsten, who seem invincible, but in practice, it's not that bad. Against Hangwul, it's enough to capture any dwarven town and wait for the opponent to attack. The Call of Urgash will allow you to block all available cells behind the castle wall; you just need to try to destroy the catapult before it breaks through one of the walls. And then gradually kill the enemy units one by one in a devilish chain.*
Also, Remix in his walkthrough of this map showed how easily you can cut down most of these bosses' armies with deliberately trained necromancers.