Play as Inferno.

I don't visit here often, but I decided to share my thoughts.
I confidently state that in the late game, Demons beat EVERYONE, except for a ridiculously overpowered Winghorn.

Justification: gating and monstrous initiative.

Formula:
1. Grak. No alternatives.
2. Forget magic schools. Completely forget them. Everything is decided in the first 2-3 turns of the hero, during which he must cast mass Stone Skin and Haste, and then a bard is not needed.
3. For the final battle: Fast gating, Wide Gate to Hell.
4. For neutral creatures, and also useful in the end: General Stone Skin, then General Haste, Tactics (if there are no +1 Speed Boots).
5. Thus, we get Logistics and Luck as the main skills, then Defense.
With Expert Gate, this is 14 levels – not that much.
With Attack and General Haste – 18. Well, we put another 2-3 levels as a reserve.
If the game drags on, you can, of course, also level up Darkness, depending on who you are playing against; an alternative is Leadership.
I've never played with the super ability, but it's cheating anyway.
6. If there is an alternative in terms of artifacts, merchants, etc., the main thing is initiative. The main artifacts are the Amulet of Mastery and a +20% Speed Ring.
7. Upgrade choices:
- old Imps (automatic mana drain, otherwise they might get damaged)
- new Demons
- new Dogs
- new Succubi (even if the opponent has antimagic for 1 turn, the opponent's key unit is taken out of action. It's fun against Orcs – you seduce the Executioners, and that's it, they're done...)
- old Horses (very often their Fear helps to reduce the initiative of the key unit)
- new Fiends (more initiative and speed, the rest doesn't matter)
- old Devils (also more initiative and speed, the rest doesn't matter)
8. In the first 2 weeks, we only make one upgrade in the buildings – for Dogs. We save money, sulfur, and sometimes wood.
In the second week, we only buy upgraded Dogs and don't buy anyone else – we save money. In the third week, we can buy upgraded Demons (level 2) and 1 Fiend – to sometimes reduce the defense of neutral creatures. We don't rush to buy the rest. We develop.
9. In the final battle, we gate everyone, except for the Succubi, with which we seduce the nearby key unit.
If there is an Amulet of Mastery, then the opponent is doomed. Devils also gate, and the speed of the entire gating is monstrous.

Those who don't believe, take any hero except Winghorn, put a crate of beer, and let's go to a club (Minsk). Load, for example, Armageddon's Blade. So that they don't talk about "masses" of Gnomes and Necromancers – they simply CAN'T do anything...

Playing as Demons on medium-sized maps is a true skill! I'm learning.