Immediately after the start, I recruited archers and quickly captured the Forest Alliance town. Then, without wasting time, I secured the mine and sawmill and headed towards the tunnel leading to the Dungeon Castle – I didn't risk going through the Druids due to obvious losses, so I went south, bypassing them (there are dancers and an observation tower there). Next, I hired archers in the dwelling and, without delay (I needed to do it before the end of the first week), I rushed to the orange castle – if I didn't waste time and didn't redeploy troops unnecessarily, the castle would be mine without any problems on the 7th day of the first week.
Then, I settled in – I sent the remaining elves to guard the gold mine, and with Agrael's demon army, I captured the mines in the Dungeon. I created a second hero and sent him to the top to collect everything that was lying around (this is important because to the east of the captured Elven town, there are many dwellings with elves; you can gather a decent battalion of archers – just be careful not to run into the green player). Soon, after a week or two, the most difficult battle of this mission occurred – with Agrael, I reached the garrison on the eastern branch of the Dungeon, and an Elf emerged from the surface and attacked me – both our armies were weak (the Elf had many different elementals), but I won.
That's it. There were no more difficulties. With a scout hero on the surface, I found 4-5 Elven dwellings, from which I gathered a good number of pointy-eared archers (don't even think about giving a hundred archers to dragons during a normal (non-blitzkrieg) playthrough – let them go; these valuable ears will be needed for the assault on Erathia). In 3 weeks, Agrael developed the castle to the fullest; the abundance of Cave Lords guaranteed an advantage in battle – he emerged on the surface through the southern exit of the Dungeon and easily defeated the eastern town, and then the western one.
That's it. Then, I hired an Elven heroine in the tavern, gave her all the troops accumulated in the three towns, developed diplomacy for fun, thanks to which the neutral elves started joining one after another (my heart rejoices and sings when 180 archers or 150 high druids want to join). Agrael, meanwhile, had fun – he ran around the map, leveled up, and searched for artifacts for morale.
When I got bored, I crushed the spectral dragons with one devilish hoof, reached Erathia (along the way, 200 Cerberi joined – a nice bonus), gave Agrael about 900 archers and 400 druids from the Elven army of the three towns, and didn't even notice the assault itself – the guys shot down everything that moved.
The mission takes about 40 minutes. I completed it in about 2 hours, simply because I was having fun running around the map and leveling up the hero.
Go for it!