[Twan]

I think some other nations would become underpowered on maps with caves if darkness is total/without more counters (human nations without death especially if their force is archers). And they are already weak on maps with many seas. IMO it may lead to caves map not considered good for MP, or nations like Man or Tien Chi not played on them.

For dark cave forts, I think it's a good national advantage for Agartha, and would find magical darkness normal for them even if an half-dark effect is added (but don't think other darkvision nations really need the same effect - are Atlantis and Abysia really underpowered ? always seen them having good results).