Walkthroughs for custom maps.

I was also thinking about this: since you can last until the 6th month, you should be able to gather an army strong enough to ignore all this petty squabbling and cause some trouble for the purple faction.

You were probably right. By the end of the 6th month, even with a not-so-strong army, Tazar managed to break through the first Necropolis garrison without catastrophic losses (imps and dogs don't count – they're just cannon fodder). It was definitely possible to play better, but the map was already taking its toll, so I spent about 10-15 minutes on this battle, and that's it.
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The purple faction turned out to be no match for Tazar, even though they had already amassed quite large armies due to faster development. All of his "small units" were wiped out with almost no losses (as an example, see the third picture). Only the last one was tougher, but it wasn't very difficult to deal with him. Thus, at the moment, I have eliminated all the purple units hanging around the gates, captured 4 castles, and all the resources around them.
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In general, the 7th month has begun; I have long lost almost all of my initial castles and resources, and my army has thinned out, but I can still survive (I've attached a save file if you're interested). And at the moment, there are 2 scenarios:

1) Use the quick battle bug to break through the second Necropolis garrison, capture the last castle, and spend until the 12th month building up an army from 5 Necropolises. This wouldn't be entirely fair, but "every map has its own methods."*:D

2) As you suggested: spend almost 6 months building up troops from 4 Necropolises and, by honestly breaking through the gates with the least amount of losses, try to end this "sadomasochistic" game with a blitzkrieg.