The Crystal of Secrecy does not reveal Stalkers. However, if you try to place it in their location, the crystal will move to an adjacent cell, and the Stalkers will become visible, but they will not take damage. And why do Shamans usually move earlier? Their initiative is the same – 12, but they have more stacks of invisibility. Now, about the Fairies – how do you even know it’s a Hit-and-Run attacker? For example, if it emerges from an unexplored part of the map and you haven’t scouted its troops? You deploy seven stacks of Fairies, and it destroys your entire army, and you lose. The risk is too great. Although, if it really is a Hit-and-Run attacker, it might help. In general, these questions, like “what will happen if you replace the Stalkers with a crystal?” can be easily and quickly tested in a duel.