Awesome stuff, as usual.
I just finished subbing for an MA Oceania position which shared the water with R'lyeh. I completely agree with everything you've said - if R'lyeh doesn't exist. But since it happens, here are a few comments to complement your extraordinary guide:
If R'lyeh is in the game, buckle up. After turn 25, they will dominate you, so kill them immediately.
Picture this: your Grand Army is swimming to meet the Alien Army. But just before the confrontation, 6 of your 10 commanders get zapfried by mindhunts, including the stealty S1 Spectre that was protecting them. So you arrive at the battlefield at half strength, across from a huge hoard of mindless chaff...
Turn 1: a half dozen ichtycentaurs get their minds enslaved, 2 dozen first strikes are spent killing them, as are a few errant numbness-es. Turn 2: repeat, only now the chaff have engaged you.........Eventually your exhausted ichtycentaurs break and retreat into enemy territory, since Imprint Souls can target underwater provinces.
I recommend:
(A) Surge out the the water looking with the singular goal of finding
indy astral mage provinces. Forge swim trunks and institute the buddy system.
(B) Beg/Borrow/Steal all the
Starshine Skullcaps you can. Put them on A and start every party with Antimagic.
(C) Beg/Borrow/Steal all the
Amulets of Antimagic you can. Use 16+4=20MR Bishop Fish to lead your underwater armies, lest you arrive at the field without any troops. Make Lead Shields if necessary.
(D) Get
Foul Vapors immediately...I know Alteration is awesome for Oceania, but you MUST get this spell before R'lyeh gets Enslave Mind. Unintuitively, Foul Vapors is castable underwater, and you can cast Poison Ward to mitigate the damage to your troops, he can't. Splurge those Earth gems on some un-mind-burnable, regenerating, poison-immune, zero-encumberance claymen to bolster your frontline.
(E) You need
Bloodstones badly, as your Mermages can't wear Earth Boots underwater. Make it a priority, as you can then use Summon Earthpower and get Strength of Giants/Legions of Steel/Weapons of Sharpness underwater. Plus you can then summon Troll Kings.
(F)
20 PD in each retreat route.
(G)
Don't cast Shark Attack in round 1. Script your Sirens for (Summon Water Power)(hold)(hold)(hold)(Shark Attack) so that the Enslave Minders are too exhausted for sustained enslavment of your sharks.
One last thought:
Sailor's Death (W3, AOE=1, 14+ AN damage) works underwater against troops that are there by unnatural means (i.e. Sea King's Goblet, Wave Breaker, etc)...Summon Waterpower makes every mage you have W3, and most get Eagle Eyes...exploit this.
Again, great stuff.