Help vs LA R'lyeh

[Zenzei]

Thugs/SCs are definitely way to go and I suggest using GoRed gargoyles(fairly easy to do with LA Ulm). Gargoyles are lifeless and mindless which makes them immune to LOT of nasty stuff, just kit them out with anti-chaff and MR items.
Beware stellar cascades for it's the best thug/SC killer in the game imo.

Regarding the attack underwater, just pillage each and every province you manage to get under the waves because you can't hold them for long anyway. Also remote bombard sea provinces with plagues and such in order to ruin R'lyeh's economy.