[Update #2]: The time has come, Creative Assembly has finally unleashed a gameplay preview showing off a battle between Nurgle and Slaanesh. Needless to say, the Nurglings look awesome!
[Update]: The newest developer update has now revealed the entirety of Nurgle's army roster. Unsurprisingly, they're quite a jovial bunch!
After a fair bit of buildup, Creative Assembly has recently begun teasing Total War: Warhammer 3's final two launch factions. Unsurprisingly, the dynamic duo will be none other than the Dark Prince Slaanesh and the Lord of Decay Nurgle.
While Slaanesh is still shrouded in mystery, I'm happy to say that thanks to the newest developer update we now have a pretty good idea of how Nurgle's campaign will function! Needless to say, it'll involve a lot of plagues, a lot of demons, and I can only assume a lot of manic cackling as well.
First and foremost, Nurgle's buildings will be completely different from the usual Total War ones. Instead of having to upgrade them in the traditional sense, Nurgle's buildings will grow, flourish, die and be reborn in cycles. The further along the cycle the building is the more benefits you'll get, and the better units you'll be able to recruit.
Speaking of which, Nurgle won't be recruiting units in the standard way either. Instead, groups of demons can be summoned directly into your armies, though they will arrive weakened and will need a little bit of time in order to fully replenish - something the Nurgle faction is very capable of buffing. Early on this recruitment system will likely pose a bit of a challenge as your emergency armies will be rather weak, but as the campaign progresses you will be able to fill and refill armies at an "alarming rate."
As you might expect, most of your Nurgle campaigns will also revolve around the Plague Cauldron - a special system that lets you devise and spread horrifying plagues. At the start of the campaign you'll only have a couple of options to mess around with, but as you progress and unlock new ingredients you'll be able to cook up everything from the Black Plague to the fan-favorite Nurgle’s Rot.
You can spread these maladies directly by using them on your armies or cities, or through the use of plague cultists. Plague cultists will be the more expensive option, though their success will be guaranteed. Once a particular plague is set loose onto the world it'll spread passively between nearby settlements and armies, as well as through battles with affected armies.
Much like the rest of the Chaos gods, Nurgle will also have access to the Unholy Manifestations and Cult mechanics. Unholy Manifestations are essentially rites that get unlocked by having a certain level of global corruption for your chosen Chaos god, while Cults allow you to create special buildings in other faction's settlements if there is enough corruption present.
For example, one of Nurgle's Unholy Manifestations is called Exponential Growth and it increases growth in a local province by a staggering 200, while also decreasing recruitment costs by 20% for a single army for three turns. Cults on the other hand have much smaller effects, mostly focused on increasing the effectiveness of your plagues, though they can also be sacrifices to plague the city itself.
All of this is just the tip of the iceberg, so if you're curious about all of the details I'd recommend heading over to the Total War website to learn more. Enjoy, and I'll make sure to let you know once it's Slaanesh's turn.