When you want to play with Multiple Generals, if not specified, the following rules applies to choose your army
Maximum Points: Players should agree on a points limit.
Detachments:
Maximum Number: Unlimited
Limitation: None except that Apocalypse Formation, Adamantine Lance Formation can not be used.
Unbound Army can neither be used.
Lord of War can be used if they represent less than 25% of the whole army, which mean one player could have a Lord of War accounting for more than 25% of his points.
Warlord: Player in the same army should agree on only One Warlord, his detachment is the Primary Detachment.
Army sources:
You can not use any of the following armies:
Space Marines Chapters & their descendant chapters: Ultramarine, White Scars, Raven Guard, Imperial Fist (including Sentinels of Terra) , Salamanders, Red Scorpions, Carcharodons, Raptors, Executioners, Mantis Warriors, Red Hunters, Star Phantoms, Fire Hawks, Astral Claws (included Tyrant's Legion), Dark Angels
Chaos Space Marines Legions: Black Legion, Crimson Slaughter, Cypher, Old Renegades and Heretics (Imperial Armour 5,6 & 7) are outdated.
Astra Militarum Regiments: Elysian Drop Troops, Tallarn Regiments
Others: Mephrit Dynasty, Farsight Enclave, Craftworld Iyanden
You can use any other sources.
Note:
Armoured Battle Group, Space Marine Siege Assault, Ork Dread Mob can be used.
Lord of Wars includes Forge World Ones:
If one army does not have a Lord of War, use Supplement-Escalation rules: +1 on Seize the Initiative roll, special Warlord Trait, and additional Victory Point
Remember that the Imperial Knight is NOT a Lord of War.
Ally:
Depending of their Camp (Order or Destruction), Players can choose Detachments of any of the following factions.
Order:
Space Marines: Minotaurs
Space Wolves
Inquisition
Grey Knight
Imperial Knight
Assassin
Space Marines: Black Templars
Adepta Sororitas
Eldar
Harlequin
Eldar Corsairs
Astra Militarum
Destruction:
Necron
Maynarkh Dynasty
Angel Revenant (As Blood Angels): + Necron Illuminor Szeras as a Mandatory HQ (Mechanical Augmentation can target any Space Marine)
Chaos Space Marine
Renegades and Heretics
Dark Eldar
Harlequins
Eldar Corsairs
Tau
Daemon
Ork