The enemy has about 5 Cyclops left. I was attacking them from a distance with Weavers, Liches, and Pikemen, and also attacking them up close with some other units, so much so that the game kept displaying the message: "5 Cyclops will die" each time. I calculated that out of the 5 possible Cyclops, I killed 20, but they were all still standing, and then they eventually fell anyway :). This is something to think about. It's still useful to carry trophies in your army. Just a little bigger, say, 10 Cyclops.
Well... you wasted your attacks. A Cyclops only dies when its turn comes. Check if regeneration or some other ability that reduces damage is active on the Cyclops, and if so, to what extent (right-click on it and hover the mouse over the corresponding icon).
Then, attack until you kill the actual number of units. If there are 5, then after firing with Succubi (6 units will die), you can forget about them and concentrate on other units with other ranged and melee attackers. The Cyclops will die as soon as their turn comes.
Attacking them with everything you have, even though they keep standing, is pointless and definitely makes you think... "maybe we should read the game description?" ;)