First my compliments to Baalz's EA Mictlan guide, consider this an add to his great great guide since I won't be going on about everything, I'' try an fill in some gaps.
Baalz's guide
http://forum.shrapnelgames.com/showthread.php?t=33753
Everyone knows that a Fire/Water bless works best for Mictlan, so no need to change that, although I like to take a higher dominion, possibility of dom kill and for the beast bat factory. You'll have no problem expanding since you're making an expanding party every single turn. There are just a few nations that can pose a problem for Mictlan early on so once you meet your first neighbor attack him. Remember Mictlan is a rush power and you need to get that extra money and blood hunting province ASAP.
Money isn't a problem at first, however as Baalz said you'll need to consider every gold piece you spend. You'll most likely be taking 2-3 provinces a turn, that should give you enough gold to make those first forts, make them in forest since they're cheaper, and by turn 20 you could have 5 forts with labs/temples. You'll be making 50 jaguar warriors a turn, and that's enough to steam-role anyone. For troops ONLY sacreds, maybe a few warriors in front for arrows but that's all, no wasting gold, for mages Mictlan priest. They cost half as Nahauli and are sacred, and you'll need them for those small expanding forces. Nahauli aren't bad they just cost a lot more, aren't sacred, aren't priests and lack evocation spells, but can be used in some situations.
In your capital you'll want to buy as many Moon Priests as possible, and I stand firmly by this, if anyone disagrees they're wrong. Yeah, you'll want a couple of rain/nature priests for site searching, however Nahauli can site search nature also, and a couple of Sun Priests for divine bless and to summon jaguars when needed. Moon priests are you best mage force, you'll need them to send lesser horror, which is a good and fast way to take out an enemy, you'll need them later for mind hunt and to stop mind hunts, you'll need them against SC's also, golems and other astral SC's to teleport and magic duel, and you can even teleport and life to life someone with them in dire situations. Having them cast a stream of horrors in a battle is also dreadful if you can direct the horrors with horror mark.
Mictlan is the best blood nation in the game no doubt but you never have enough blood slaves to go around, plus you'll be using blood slaves in battle sometimes and nature or death gems can't die to arrow fire nor do they become troops once you retreat? They have tons of great stuff to spend their blood slaves on and the main problem is to decide how to spend them.
Now, I see it like this, at one point of the game you will most likely want to switch to blood hunting as much as possible. You should be using every 3.5-7K province for blood hunting and even when you're pulling 200 blood slaves a turn it isn't nearly enough.
You can either decide to go for soul contracts, however you should be giving them to Moon Priest since they horror mark you so you can script returning, another reason to buy Moon Priests. Having a free spawn army of devils is great, they have high HP. good MR so can't be banished easily, two attack and one of them is magic, paralyzing attack. They make a hell of a raiding party against anyone and can bring down some SC's not immune to poison. So one thing definitely worth considering.
One thing to keep in mind here, forge hammers don't work on soul contracts.
You can focus more or Jaguars. They are wonderful, high HP, 3 attacks, good strength, darkvision 50 and are sacred! They also have 25 action point which is a great advantage over beast bats (will explain later ). The problem with them is even though a level 4 blood spell, you will find it dificult to use them early on. Sun priests can lead 15, moon/water/nature can lead 10 and Micltan priest only 5, and they are your main source of mages. So before you can get some banes to lead them their usage will be limited.
Another useful summon is Civateteo, you'll need to get Onaquis before you can summon them since they're death/blood but they make good stealthy thugs,
Sacred, etherial, fear and a life drain attack. Put a wine shield and any armor and send to raid some provinces.
Now we come to Onaqui. Saving blood slaves for them can be painful, looking at those 1000 blood slaves in your lab and not using them makes you question yourself, but I think they're the best option. Why would I think that? You need to get to const 6 with Mictlan first for lanters, blood boosters and boots of youth and since you're on 6 you'll want to try and get first to 8 for the chalice, you need to summon a Couatl to forge the challice and he's on conjuration 6, you'll also be making a few stops for site searching spells. And Onaquis are blood 7! Ain't no way you can do all that before turn 40, but by that time you'll have hundreds of blood slaves saved up for Onaquis and your sacreds should have been enough to keep you safe. Now start making those blood boosters and summoning Onaquis at 100 blood slaves. In no time you should be getting 50 beast bets a turn, you'll also have Sun Priests with 2 boosters to cast infernal disease when needed, and you'll be able to send lesser horrors with Moon Piests, which is a fast way to concur someone, or at least drive him crazy.
Onaquis have some paths you need, death mainly. They are your way into Tartarians. They should be sitting home (in high dominion provinces), auto summoning beast bats and banes to lead them, casting rain of toads to shut down enemy forts, and forging some items you'll need. Dusk dagger and alike.
Those free beast bats can really make someone suffer. Sacred, paralyzing attack, good attack/defence, not bad on HP also, 19, stealthy and blind. Now this is something very interesting, maybe a little hard to pull off but still, if you can give a Civateteo 2 death boosters for darkness and get your hands on unholy sword for holy bonus to cast divine blessing, you can make one hell of a surprise massacre. So, what's their biggest problem? Only 3 action points, but who the hell cares if they're fliers. Well if you give a staff of storms to someone, you can say goodbye to those beast bats. They practicly won't be able to move and arrows will massacre them. That's why I believe Cealum is Mictlans nb.1 enemy. Storm + wind guide + easily massed archers + thunder strike... And for early game, what better spell than seeking arrow? Trust me this is your acheelis heel. The one way to stop those damn thing is to bring along scouts to catch those seeking arrows. Mictlan really lacks air magic.
Oh and also a very important national hero for Mictlan, Eagle priest, he has 3A1B. Important since he gives you the paths you need for robe of the magi. Forge staff of elemental mastery with pretender give to Eagle priest for bag of wind or winged helmet, give blood booster and empower to blood 2, only 30 blood slaves. Now getting those Tartarians with robe of magi and ring of wiz/sorcerry will be much easier.
So you'll even be able to summon Air Queens besides Fire Kings, and Water Queens. The Only thing you lack is Earth Kings but possible, you still have a good shot of getting Podession if you find a earth 1 indie mage. Empower to blood, forge blood stone, than earth boots, pebble skin suit ( people rarely make this ), and use that staff of elemental mastery. Now you can even summon
an Earth King, or first Podession and the Earth Kings with him.
With a little luck you have all the elemental royalty covered, a way into a Tartarian factory, a free spawn army of beast bats and devils, stealthy thugs.
If it's a CBM game you can summon hundreds of Bone fiends for next to nothing ( overpower spell IMO ) 13 for 3 blood slaves. Good strenth, two attacks, 15HP. Use those Onaquies to summon a legion of them, cast mass protection and you've got a strong cheap army.
Streams of horrors to stop enemy armies, either directly or to cut off their retreat province and to take his provinces with horrors and scouts. Infernal disease for unguarded commanders. Astral corruption is possible even with a moon priest, robe of magi + ring of wizardry + ring of sorcery + astral cap + blood thorn = 6B6S
Tlaloques can come in handy also, good stats, can make cast murdering winter and other useful stuff, however a little expensive I think, 60 water gems.
Mind hunters with +5 penetration bonus, forge rune smasher with pretender.
Flames from the sky, living fire, living water against nasty SC's. You'd be surprised how fast they can tear apart almost anyone, and you'd be surprised how many a F9W9 pretender can cast. And on top of all that how about a F9W9 Moloch with awe for pretender? Yeah, I know, overkill.
So is there anything Mictlan lacks? Yes, some heavy evocation but I think they can get by without it.
Another thing to keep in mind, people are scared of Mictlan so keep a low profile when playing them, keep your beast bats in hiding, don't waste gems on useless items/summons and always be prepared to get teamed on and you'll do fine.
And don't forget you can summon Demon Lords with Onaques with some boosters, the blood skull, blood thorn, armor of thorns, and a unique item like book of lower plains, or black book of secrets.
Here's a nice detail I forgot.
Once you get to Onaqui, you best summon, you'll have access to death magic.
If lucky maybe you'll have some death gems stashed and a fair death income before Onaqui, so anyway, Spectres are what I have in mind.
They go very nice with Mictlan. They do cost a big 20 death gems, but it's worth having a few around, before you get tartarians. They can give you earth/astral combined, that's a crystal coin for the moon priests to mind hunt. You can forge eye of void with moon priests, and spell foci, and you have you water/fire pretender for rune smasher.
Spectres are also stealthy, ethereal and have a life drain attack. They can also teleport with boosters, can't be mind hunted, can't be magic dueled since they can go into hiding, or just cast returning, and can summon golems.