Manuals for playing as Dungeon

The English original of the guide hasn't been updated, so there's no point in updating this one either. Moreover, many of the things written there are quite ambiguous.

But with a small stack of upgraded Furies appearing in your army (starting around week 2), keeping melee Assassins around loses its meaning.

I disagree; ranged Assassins are very ineffective due to the penalty for ranged attacks, resulting in damage being only a quarter of what it should be in most cases. When I tried playing with them at the beginning of the game, it always came down to pressing "Ctrl" and engaging in melee combat; otherwise, the losses are simply terrible. Hunters are better in this regard; they only know one thing, and they do it better than Assassins.

And is Summoning Magic really worth learning? It always seemed to me that it's better to use Chaos to deal damage or max out another useful skill. A request to those who actively use Summoning: please write how and in what situations you use it. Approximate spell costs are welcome.

Chaos is good at the beginning of the game, while Summoning is better towards the end. Dark Elves are excellent summoners due to their high magic stat. Summoning consumes a lot of mana. Elementals cost ~15 mana (I don't remember the exact numbers), and a Phoenix costs 20 and a bit. But firstly, specific skills from the Sorcery branch, which are easily obtained by Warlocks, will significantly reduce this number. Secondly, not every battle requires frequent use of summoning spells; it's possible that summoning a Phoenix and Elementals once will be enough, even if the battle is difficult. In general, I am a supporter of this school of magic.

I used to always take Sinithar and win by using his ranged attack, but his late-game specialization is disappointing.

In reality, you can take Sinithar for a quick start, but then switch to someone more promising (level them up in parallel).