Grand Alliance: Chaos
Because leaving a job half-finished isn't his style (and to continue his streak of being more successful than some other prominent chosen of Chaos), Archaon, now promoted to "the Destroyer of Worlds", returns with a souped-up Dorghar to give the middle finger to Sigmar and bring Chaos to all the Realms.
Beasts of Chaos
Basically the old Beastmen, with your Brayherds, Warherds, Monsters of Chaos, and Dragon Ogres.
Chaos Giants. Same as normal Gargants, just a bit hornier.
Archaon and his Varanguard entourage.
The Clans Eshin - Still sneaky and killy.
The Clans Moulder -
The Clans Pestilens - (Former) Nurglite allies. Currently butting heads with Skryre to decide who gets the most power.
The Clans Skryre - Are the first ones to decide to try and use Realmstone as well as Warpstone to power their weird science things. Butting heads with Pestilens over influence.
The Clans Verminus - The clanrats, stormvermin, and other footslogging troops.
Masterclan - Rat-Illuminati. Manipulate the Council of 13 behind the scenes.
Blades of Khorne
Daemons of Khorne -
Khorne Bloodbound - Bloody Warriors of Chaos with bloody Khornate theme.
Maggotkin of Nurgle
Daemons of Nurgle -
Nurgle Rotbringers -
Disciples of Tzeentch
Daemons of Tzeentch -
Tzeentch Arcanites -
Hedonites of Slaanesh
Split into Slaanesh loyalists, Archaon-worshipping daemons and factions of usurpers.
Slaves to Darkness
Classic Chaos Warriors and Marauders go here, with a fair bit of room to synergise due to being able to choose their deity keyword. Still technically includes good stuff like the Chaos War Mammoth.