Grand Alliance: Death

Marching beneath the black, decrepit banner of Skeletor Nagash, Lord of Undeath, the rotting hordes of Death seek to swell their ranks and expand their influence on the Realms.

Deadwalkers

Zombies, Corpse Carts and Dire Wolves. Not much else to say but mind the smell. While not so effective on the tabletop except in large numbers, lorewise every zombie can potentially cause a zombie apocalypse; everyone killed by a zombie becomes a zombie, rinse and repeat and not just humans. Tactics page here.

Deathlords

Nagash and friends. The elite guys of the Death Grand Alliance, where every special named character hangs out. They also have their undead angel-gargoyle bodyguards. Vlad von Carstein and Settra the Imperishable are conspicuously missing, and much-missed. Tactics page here.

Deathmages

The crusty Necromancers who actually did well out of this whole "end of the world" arrangement, finally being independent of the Vampires, and having enough room to spread their feet across an entire realm to boot. Tactics page here.

Deathrattle

It's the skellies, ready to help you bone your opponent until they like it. General bare-bones skeletal infantry and cavalry overseen by Wight Kings, who are now generally evil kings who were overthrown or assassinated in the realm of Shyish, coming back by sheer dickish willpower to dominate crumbling ruins of their former kingdoms. While a fairly small list, there's another option if you only want to run a skeleton crew - make sure to pick up some units from the Tomb Kings entry listed below. Many of their unit entries have the DEATHRATTLE keyword (and some, like Settra and Necrotechts, can buff/synergise well with them), and by combining the two you can get a nice full and fluffy list. Tactics page here.

Flesh-Eater Courts

The first Death faction to get their own Battletome, the ghouls have been refluffed, and in quite a cool manner, too. Now, they see themselves as honourable subjects of a benevolent kingdom, blind to their true form and behaviour. Those two cannibalistic monsters snarling and fighting each other over an old woman's legbone? Just a couple of old friends having a polite haggle in the market over a loaf of bread. The most vicious, terrifying of their number flying atop a massive, decaying zombie dragon? Their great and kind king riding out atop his noble steed to war against injustice, of course.

Nighthaunt

Spooky ghosts. Also the Black Coach. Generally trollish and annoying to kill due to their ethereal-ness, it also includes the absolutely disgusting Mourngul.

Soulblight

It's the Vampires Soulblight! It's all your classic (and mostly dated) vampire models. Even the classic hero models are here, only now completely bland, generic Vampire Lords instead of actual characters. See more here.

Other

Tomb Kings (Warscrolls Compendium: Tomb Kings[1]) - Poor, poor Tomb Kings. Discontinued and all but absent from mention in the fluff (apart from Neferata fucking around with "Nulahmia"), what could possibly save them from such disgrace? Being disgusting on the tabletop, that's what. Some GW guy obviously took pity on the not-Egyptians and gave them a great list, making them popular in tournaments and their models have become even more popular. So why did GW not want to make money from this again?