Hero = Zoltan, level 25-26
Chain Lightning is great against Orcs. But while the hero is casting, we get pummeled. The key is to prolong the battle and give the hero more opportunities to contribute.
Here's the strategy:
Skills:
Education + Logistics = Keen Mind + Attraction
Defense = Ballistics + Fortitude
Magic = Distraction
Darkness = Pain/Mind/Earth
Battle (based on the hero's turns): the army stays in place, and if possible, moves out of the way of attacks:
1) Cast Subjugation on the Assassins. Deploy Centaurs.
2) Then, Berserk.
3) If the hero gets a 3rd turn and Subjugation and Berserk are active, cast Mass Slow.
4) Repeat actions 1 and 2.
The result is that the Orc will defeat himself.
In total, the Orc will take quite a long time to reach us, and it will take him 2-3 turns to eliminate one of our stacks.
I also advise destroying his wagon with Liches and stealing ammunition from the Centaurs if you decide to eliminate them early. Although this is a priority.
Troops (by level):
1) Elite Archer (no point in regular Archers, +defense against Centaurs and Cyclops + Silence)
2) Elite Archer (will last longer)
3) Elite Archer (but you can also use regular ones if it works; if so, we can reach the Shamans)
4) Elite Archer (if you throw regular ones into battle, there will be no response, but we will lead them to the enemy, and they will be defeated. Elite Archers can also Stun)
5) Elite Archer (maybe thanks to them, we will last even longer)
6) Elite Archer (attacks without response)
7) Elite/Standard (Mournful Strike/immediately reduces the defense of his entire army by 1). It's up to you to decide what's more important.
The above has been effectively used in practice.
There is an option to take a Dryad and go into Chain Lightning. But in reality, it's not a fact that the enemy will spend more time on us because of Chain Lightning than with the strategy described above. I tried it once... it turned out to be the opposite