Two sisters.

I played through the most difficult part of the game without killing the Necromancer (I didn't want to waste time, and I also didn't know about the bonus – an increase in troops). Instead, I used diplomacy + the Leadership Crown – the most powerful tool for fighting enhanced AI in long-term maps. It allows you to classically overwhelm the enemy with numbers (or successfully counter a large number of enemies). Dark Magic is not extremely necessary under these conditions. With good, strong troop stacks, it can be replaced with Summoning Magic, and you can play defensively, hiding in your Castle, first destroying the ballista, and then, with one shot (or offensive magic), destroying the ammunition cart (note that the Dwarves' archers have very few shots, meaning that without the cart, they quickly lose their combat potential). Even if the AI breaks through the wall, the entire interior space of the Castle must be filled with troops placed correctly – so that there is no room for flying units to move. This is easy to do without Summoning Magic, and even easier with it – place crystals and walls of swords on the free squares. At the point of the breach in the fortifications, place a wall of swords or a Phoenix under the protection of Light Magic – for regeneration. As a result, the AI's troops will be idle at the walls, unable to push through the narrow passage with their strength into the Castle. The main thing here is to have archers of your own. The AI is programmed in such a way that it often makes its first ranged attacks with its upgraded units (Chain Lightning, etc.) specifically against them. This is where luck comes into play. You will either have to replay the battle many times, waiting for the AI to randomly choose another target, or use Dark Magic to force the upgraded units out of the attack (Dominate, Berserk, Blind). Preserving your own archers and quickly destroying the ballista is the foundation of defensive tactics in the city.