At the start of your Shooting phase, the Dark Apostle from the Brethren of the Dark Covenant can scream a litany of rage and bloodshed instead of shooting. If he does so, each other unit from the Formation that is wihin 12" is filled with unholy zeal, and gains the Zealot and Feel No Pain special rules until the start of your next turn.
A unit containing one or more models with the Zealot special rule automatically passes Pinning, Fear and Regroup tests and Morale checks, but cannot Go to Ground and cannot choose to fail a Morale check due to the Our Weapons Are Useless rule. If a unit gains the Zealot special rule when it has Gone to Ground, all the effects of Go to Ground are immediately cancelled. In addition, units containing one or more models with the Zealot special rule re-roll all failed To Hit rolls during the first round of each close combat - they do not get to re-roll failed To Hit rolls in subsequent rounds.
When a model with this special rule suffers an unsaved Wound, it can make a special Feel No Pain roll to avoid being wounded (this is not a saving throw and so can be used against attacks that state that 'no saves of any kind are allowed', for example those inflicted by Perils of the Warp). Feel No Pain saves may not be taken against Destroyer attacks or against unsaved Wounds that have the Instant Death special rule. Roll a D6 each time an unsaved Wound is suffered. On a 4 or less, you must take the Wound as normal. On a 5+, the unsaved Wound is discounted - treat it as having been saved. If a unit has the Feel No Pain special rule with a number in brackets afterwards -Feel No Pain (6+), for example - then the number in brackets is the D6 result needed to discount the Wound.
If you wish, you can say that any Chaos Space Marines Detachment or Formation is also a Black legion Detachment or Formation. Detachments and Formations drawn from the Crimson Slaughter may use the Warlord Traits and Tactical Objectives from the Crimson Slaughter supplement in addition to those in C:CSM and BRB.