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Forget about Krag, he's not very useful! Let me explain why: only at level 31 can the hero kill 1.5 creatures of level 7, plus Krag's ability, meaning at level 31, 3 creatures of level 7 die! If you upgrade the Devil's Strike skill, there's only a 30% chance that the damage will be doubled, and a 70% chance that it won't! And what do we get when we reach level 31, which isn't that easy and takes more than a month to achieve? We get a 30% chance of killing 6 creatures of level 7!!! It's much wiser to use the same Scare skill to frighten units, or increase the attack of all troops by +15 already at level 30, and add even more Fury – that's a huge bonus!!! And you should always choose a hero based on the unit, as this is a very significant bonus in the final stages!!! So, choose Tilseck, because Barbarians are usually not targeted; they are slow and left for last. In 3 turns, they will have so much Fury, plus the unit has the Fury skill, which gives them such a high attack and infinite doubled damage, and by that time, the runes will be used up!! He simply won't be able to kill them all on his own!!!!