Please remember that this is still early information and as such is still considered to be rumor until the release.
via an anonymous source on Faeit 212
here are the formation
The Beast Waaagh!
Grimgor Incarnate, 2 units of black orcs, orc boyz and Ogres, plus 1 unit of orc boar boyz, , ironguts, and leadbelchers, and 1 giant.
Orcboyz and Orc boar boyz must be upgraded to big uns
No units in the formation take animosity tests
All units benefit from waaagh and can re-roll one or more dice for charge range.
The Host of Shadow
Malekith, 1 unit of black guard, phoenix guard, wildwood riders, darkshards, black arc crusaders, high elf spearmen and a War Hydra.
no units have to take dangerous terrain tests and shooting attacks against Malekith or units within 12 are at -1 to hit
Increases Steed of Shadow to 36, and can do so multiple times.
Host of Life
Alarielle, Durthu, nasetra and arahan-must be mounted, 1 treeman ancient, 1 handmaiden, 1 sisters of avelorn, 2 glade guard, 1 deepwood scouts, 1 wild riders, and 3 units of dryads.
all units have regeneration, Durthu and treeman ancient get hatred against any enemy unit within 12 of Arielle.
Host of Light
Tyrion, Imrik, 2 high elf princes, 2 knight orders, 1 reiksguard, 1 demigryph knights, 2 lothern skycutters, 2 silver helms, and 1 unit of cold knights.
Gain +d3 result in close combat if they charged this round.
Hatred towards daemons and undead
The Blood Hunt
Wrath of Khorne, bloodthirster Insenate Rage, and 1 unfettered fury, 3 units of bloodletters, 1 of bloodcrushers, and 2 of flesh hounds.
d3 units get vanguard deployment rules
all have hatred and can re-roll failed charges.
Army of Blight
Isabella, great unclean one, 3 units of plague bearers, 1 of plague drones, and 2 units of nurglings.
enemy units have -1 leadership, their generals inspiring presence is reduced by 6", and shooting attacks a -1 to hit.
The Host of Death
Nagash, Arkhan-mortarch sacrament, Krell mortrach despair, 1 unit of Morghasts, Morghasts Archai, Grave Guard, and Black Knights.
Arkhan get a +3 bonus to casting results
Grave Guard and Black Knight have WS5 and suffer two less wounds from unstable.
Host of Fire
Caradryan, 2 units of Asuryan, 1 unit of white lions, Har Ganeth executioners, and eternal guard.
Asuryan must take flamespyre
All models get devastating charge and flaming attacks
Wake of Fire at +1 strength
Throng of Metal
Balthasar Gelt, runelord, 2 units of thunderers, 1 unit of irongdrakes and ironbreakers, 2 cannons, 1 organ gun. 2 gyrocopters
+1 armour piercing and saves
on a 5+ warmachines and units armed with ranged weapons can shoot again.