Heroes of Might and Magic V [Game Discussion]

The "Ranger" campaign. The hero Faidaen, with his elven army, initially fought as usual: if the battle is in manual mode, then all shots and attacks must be controlled. But at some point, at the beginning of the battle, the archers and druids started shooting at some target on their own, and then the battle continued as usual, under the control of the player. There is nothing about this "first strike" of these units in the hero's abilities or equipment bonuses. What is this ability, and where does it come from?