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 the 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:
■ [LETHAL HITS]
■ [SUSTAINED HITS 1]

Leader

Before the battle, in the Muster Armies step, for each leader and support unit in your army, you can select one friendly bodyguard unit that unit can lead. That unit will then lead that bodyguard unit for the battle and form an attached unit with it. Unless otherwise stated, each bodyguard unit can only have one leader unit and one support unit attached to it.

Profiles:

Abilities
Leader: This model can be attached to the following units: ■ ACCURSED CULTISTS ■ CULTIST MOB
Faithful Flock: While this unit is leading a unit and contains a CULT DEMAGOGUE model, models in that unit have a 5+ invulnerable save.
Dark Ritual: Once per battle, in your Command phase, if this unit contains a CULT DEMAGOGUE model, it can use this ability. If it does, until the end of the turn, this unit can declare a charge in a turn in which it Advanced and each time a model in this unit makes an attack, add 1 to the Hit roll and add 1 to the Wound roll.
Disciples of Be'lakor: This unit has the Dark Pacts army rule, and can use it as described in Codex: Chaos Space Marines, even though your Army Faction is not Heretic Astartes. If this unit is Be’lakor, it automatically passes the Leadership test required for Dark Pacts. Shadow Legion Heretic Astartes models in this unit have the Deep Strike ability.