Gameplay tactics on the large map.

Yesterday, I was playing with a friend in a strategy game; he was playing as Deleb, and I was playing as Nur. Right from the start, he got the "Secret Defensive Cloak" artifact (an item that provides resistance to water and ice) – as a result, "Deadly Cold" dealt 1005 damage (to the ballista's health) instead of 1100. This was one of the factors that led to our defeat in the final battle.

So, fellow warlocks, keep this in mind: artifacts that provide resistance to ice don't allow you to destroy a machine in one cast (maybe this is common knowledge, but it was a revelation for me, and it might be useful to someone).

I tested this in duel mode, and it's indeed a bit strange. I tried using this perk against heroes with "Secret Defensive Cloaks" (25% resistance to ice) and "Flame Tongue" (50% resistance to ice). With the "Whip of Cold," it didn't destroy either the machine or the level 7 creatures. With the cloak, the results were inconsistent. Sometimes it destroyed level 7 units, even though it shouldn't have based on the amount of damage, but it didn't destroy machines. In another case, it was completely unclear. "Deadly Cold" destroyed the ballista but left the tent with a few hit points, even though it shouldn't have destroyed anything based on the normal damage.
I think this is how it works. In general, the perk itself deals additional damage in the form of + the health of one creature, but artifacts reduce the total damage. If the damage reduction doesn't negate the excess damage, the perk destroys one creature or machine, but if it does, it doesn't destroy anything, but it still deals more damage.
For example, a ballista has 1100 health with expert machines, and let's say "Ice Bolt" deals 500 damage. With the perk, it adds another 1100, resulting in 1600 damage. The enemy has a cloak that reduces ice damage by 25%. As a result, instead of 1600, it will deal 1200 damage. This is enough to destroy the ballista. But if the damage from "Ice Bolt" is 200, with the perk, it will be 1300 damage, but with the damage reduction from the cloak, it will be 975 damage. As a result, it's not enough to destroy the ballista, and it will survive with 125 health. That's the story.

Judging by your post, "Deadly Cold" should have dealt 1340 damage (240 + 1100 from the perk), but with the -25% reduction, it dealt 1005 damage, and that's why the ballista survived.

But it's clear that the Shadow League has less chance of ending up in this situation, as they penetrate magic defense, even if only partially.