What kind of cheaters are they! Is everything done according to the rules? And do you think where the dead from the battlefield go? So be glad that not all units turn into skeletons (by the way, in the 3rd game, you could even resurrect vampires), but here only skeletons.
I recently fought against royal griffins, and they flew away every turn - they decimated half the army - that's what I call cheating: there's no unit, but then it hits like thunder, and you suddenly find yourself short of hundreds of skeletons...