Top 10 MP races?

[Turin]

Caelum is clearly the best. You just need to find one indie site with random mages(preferably loremasters) and your nation has no weakness and tons of boni.

What makes Caelum the best?

[Turin]

Well you get lots of free picks due to +3 cold preference, your mages are the cheapest AND the best(for combat at least) of all nations. You will get the airqueens(best SCs), if you don´t make serious mistakes.
You can expand pretty well early on with blizzard warriors and mammoths and you SC pretender.
Other nations have a very hard time attacking you, because of the fatigue effect from cold3 and your fantastic mobility. Once you have evocation 6, you can destroy entire armies with a seraph + high seraph hit squad(seraph wielding staff of storms and ring of tamed lightning, set to retreat, high seraph casting wrathful skies/mirror image etc). Even better you can teleport that very cheap hit squad(cost 275 gold and 30 air gems) around with cloud trapeze.
Another advantage is that you can build clams as soon as you get construction2.
But mostly the cheap superior mages make caelum the top nation.

What would you advise for a Caelum Sc Pretender?

[Tuna]

Prince of Death, Nataraja.

PoD fills in nicely the lack of proper thugs, by the time you can get air queens you can also get bane lords.

Nataraja just generally rocks. Just dont forget to give him cold resistance before sending him out. (breath of winter works nicely there...)

[Turin]

In my mp game I took the ghostking with earth 3 water 1 air3 death2 and superscales(order 3 productivity 3 growth 2 magic 3 misfortune 2 and cold 3). With alteration 3 he can take almost every indie province alone without equipment(provinces guarded by deathcasters or lots of flyers being the exception).

It probably would have been better to not take so much productivity and go for death 4 and air 5, but I managed to get all the airqueens anyway.

[Graeme Dice]

All of this only holds true if your enemies aren't smart enough to put rings of tamed lightning on their thugs. Once they do that, Caelum's mages can be ignored, and you only have to worry about their pretender.