Heroes 7.5 Ultimate Edition mod for Might & Magic: Heroes VII.

Apparently, this is a faction from another Czech mod that was developed separately. It seems to have been somewhat abandoned, with only a not-so-polished version being released. It's not surprising that Heroes of Might and Magic 7.5 eventually absorbed that mod.

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But as far as I can see, they significantly changed the faction. The Hell Pits of Skaven from Warhammer Fantasy Battles somehow made their way in XD.