LBE – minimal balance changes for Heroes V 3.1.

10 mercury is probably too expensive... for Necropolis, it's an unaffordable price, as almost all buildings in the city consume this resource. As an alternative, you could make the "Castle" cost in the city individual for each faction, so that it requires 10 units of a NON-primary resource. For example, for the undead, 8k gold, 10 wood and ore + 10 units of any resource, except mercury; for Inferno, except sulfur, etc.