Their stats doesn't seem to scale at all for sub-40 civs, which makes them very hard to kill with my lvl 20 civ. This isn't too bad on maps where you can clear the whole thing then come back to the guardians, but on something like timed defense map I have to completely give up on killing them as they would completely wipe my army. Edit: Actually, I don't quite know what's going on now. When I did Elite: Lots of Rogues with my lvl 40 civ, the elephants have ~10k hp, when I did a quest with my lvl 20 civ they also had ~10k hp, but doing Settlement of Helheim (with my lvl 40 civ) they have almost 20k. I will try to take some screenshots if I come across it again.