Against which factions is it easier for demons to fight, and against which is it more difficult?

Dear sir, where do you get these numbers from? 400 Imps by the endgame – that’s the minimum! And draining ALL the mana from a Warlock is usually not a problem. Of course, if your hero has a magic resistance skill, it might not be all of it, then the summoned Imps will suck up the rest...

Player, I completely agree with you... Imps drain almost all the mana, and it can be quite difficult for the Warlock, especially since Warlocks often have low magic skills (they can't cast many spells after that)... I remember feeling this particularly strongly in the last mission of Heroes of Might and Magic V, playing as Rai’lag... So, no, when fighting demons, you need to apply more strategy...