[Zeldor]

I was invading MA Atlantis as LA Agartha in Kingmaker. There are some things you can do, but they are quite limited:

- thugs/SC, first choice, but mobility here is a problem, so best is to teleport/trapeze them in
- elemental spam! that's the best weapon for uw battles [takes lots of gems though], so living water and living earth
- getting some really tough national troops [like heavy cavalry] with water breathing gear [pricey too]

Of course you want friendly currents and sharks on your side. And many spells work fine uw too, like disintegrate, soul slay etc.