If your Army Faction is HERETIC ASTARTES, you can include any of the following units in your army, and when you do so their Faction keywords are replaced with HERETIC ASTARTES:
The combined points value of such units you can include in your army depends on the battle size, as follows:
If your Army Faction is HERETIC ASTARTES, each time a unit with this ability is selected to shoot or fight, it can make a Dark Pact. If it does, it must first take a Leadership test before any effects of that Dark Pact are resolved; if that test is failed, that unit suffers D3 mortal wounds. Then, select one of the following abilities for that unit’s weapons to gain until the end of the phase: