The most useful monster.

Cyclops are useful as ranged units. They are quite strong ranged attackers, but not very good in melee combat. If you gather 70-90 cyclops, that's a serious advantage and a good argument for victory. (And I'm not even talking about larger numbers.) But I usually don't go with such an army; I prefer a solo hero. At the beginning, of course, I have to use berserkers and centaurs. (playing as Fortress). But as soon as I feel that my hero can manage without an army, I buy a bunch of nectars and set off. It's useful to travel with a single hero. (it allows for exploration). And if there's an opportunity to "steal" an artifact or resource, it's worth taking. "Stealing" means picking up an artifact or resource without attacking the guard. And if the guard is strong, like a Champion, you can run away from the battlefield without any losses. But that's when the map is difficult. Playing as Necropolis is a different story.