Chief Librarian Mephiston

Unless part of an Attached unit, this unit can only be selected as the target of a ranged attack if the attacking model is within 12".

Units with this ability that are eligible to fight do so in the Fights First step, provided every model in the unit has this ability.

Some models have 'Feel No Pain x+' listed in their abilities. Each time a model with this ability suffers damage and so would lose a wound (including wounds lost due to mortal wounds), roll one D6: if the result is greater than or equal to the number denoted by 'x: that wound is ignored and is not lost. If a model has more than one Feel No Pain ability, you can only use one of those abilities each time that model suffers damage and so would lose a wound.

If your Army Faction is Adeptus Astartes, at the start of your Command phase, select one unit from your opponent’s army. Until the start of your next Command phase, that enemy unit is your Oath of Moment target. Each time a model with this ability makes an attack that targets your Oath of Moment target:
■ You can reroll the Hit roll
■ If you are using a Codex: Space Marines Detachment and your army does not include one or more units with the Black Templars, Blood Angels, Dark Angels, Deathwatch or Space Wolves keywords, add 1 to the Wound roll as well.