General gameplay tactics and its features.

By the way, I've sometimes encountered a situation where the AI opponent flees even when it shouldn't. That is, I immediately start eliminating its fast units, and it shouldn't have any moves left because I should be able to destroy everything in one round (and thus take its artifacts) – but suddenly, with its slow unit, it manages to escape, preventing my faster unit from finishing it off. Is this a bug, or a possible situation under certain conditions?