Bro, sea serpents + sleep clouds is a recipe for victories uw. Use mages.
All sea serpents are dead, bro (this was the last one). Survived mages are holding anal defence in capital with remaining army. And those shard guards have high MR, they don't really care about my sleep cloud. Besides, the best of Agartha's units (it's summons) are mindless. Nothing I can counter as Oceania.
The most stupid thing of me was rushing land expansion. I should have done my homework, but I didn't know how
magnificent are Oceania's surface fortifications. The idea was:
1. Pop out of water during first turns (done)
2. Build fort+lab+temple on surface before year 2 starts (done)
3. Start spammin' summoning mages and centaur cataphracts. Order them mages summon decent surface stuff for further expansion (NOT DONE).
I was naturally surprised when I realized that Oceania can't hire SHIT on surface. Either standard neutral commanders, or absolutely useless turtle warriors/turtle commanders - take your pick.
Sirens are useless too. I didn't lure anything underwater during this session. I've sent them to Vanheim, Ulm and Agartha - total immunity, everyone.
So, to stay underwater and be able to do at least something, I really needed Conj5 and Voice of Tiamat, for all my gem income needs. But by the time I finished researching this, Agartha went berserk on me. Why search provinces if they are to be conqured by enemy? No point in that.
Conclusion: don't play MA Oceania, or at least prepare some strategy in sp.