[Psycho]

AoE, you seem to be playing the same nations as I do. I have just recently finished a game with LA Man and I am playing another one with MA Caelum now. If you make a guide for Kailasa next, that will be creepy.
Anyway I wanted to give some praise, some critique and some of my thoughts. Not too much though, as my opponents could be reading this.

I disagree with taking a titan pretender. I believe that the rainbow pretender is the way to go with this nation. You lack magic diversity and are not vulnerable early on with the mammoths. The mammoths are also great for early expansion. If you fear early rush, you can always go for evoc4 and thunderstrikes as your first research goal. If you take the titan pretender just for the extra water gems, I think that's faulty. You'd be better off taking some fire and death. With all the archers you'll be recruiting (since the infantry is terrible), why not have the opportunity to cast flaming arrows. And death is death, you always need it. Also, I don't see the reason for water on pretender, your mages cover that.

No sacred mages is a problem with research, as you will pay big upkeep for your mages and thus have less of them researching. Also, since all your troops except mammoths are total crap, as soon as your opponent finds a solution for mammoths, you will have to start fielding your mages a lot, which translates to falling back in research.
Generally I wouldn't recommend owl quills as I don't find them effective for their cost, but this is one nation where I would make an exception. Compared to skull mentors you get the same amount of research for 2 gems more and you need three times more mages to spend their time forging. With Caelum you will have plenty of air gems for all your needs, so no need to worry about the first thing. Caelum also has cheap A1 mages for making quills, so you won't lose too much research by their forging. Those A1 mages are also MA Cealums most cost effective researchers, so you will want to recruit some of them. Not too many though, as there is not much else they can do.

Empowering with 50 nature gems with a nation that has no nature income and no nature mages can be problematic. Yes, it will pay off in the long run, but it will be very hard to scrape the initial investment. I guess you could summon naiads for more clamming, after the first empowerment, but that will use up lots of water gems.

I liked the idea about fear and yazatas. That's new for me. I always compared yazatas to gandvharas, they cost the same but are much weaker, so I decided I won't be summoning any of them. But this synergy you presented sounds nice. Spentas give you magic diversity, but IMO are too expensive at 60 astral pearls. It will cost you 360 astral pearls to get them all, not 300, at least in vanilla. Also, I never noticed about storm flying abilities of storm generals and storm guards, although their name suggests it. That's nice to know.

Wingless are nice to mix in with mammoths to boost their moral, but even better are longdead. You can use a high seraph with a death pick to summon a mound king and make him your prophet.
All spire horn warriors have 50% shock resistance. The storm warriors battlefield spell gives them 100% shock resistance, so you can safely use them with air evocations - thunderstrikes, wrathful skies, etc.
Flying mammoths can be nasty into the later game as well. Imagine mass flight + fog warriors + quickening + will of the fates combo.

In the end, although I think this is a nice guide, my mind hasn't changed. I still think that MA Caelum is the weakest of all three.