Leaders joining bodyguard units, and how their rules combine.
Some units have the Leader or Support ability listed on their datasheet (see below). Such units are known as leader units and support units respectively. Both of these abilities allow such units to lead other friendly units (known as bodyguard units) to form attached units. An attached unit is a single unit for all rules purposes. Leader and support units can only lead specific bodyguard units, as listed in the Warhammer 40,000 app.
Each time an attack targets an attached unit, if that unit contain one or more bodyguard models, use the highest T characteristic of the bodyguard models in that unit while resolving that attack, even if a leader/support unit in that attached unit has a different T characteristic. If that unit only contains leader/support models, use the highest T characteristic of those models while resolving that attack instead. Rules that are triggered when a unit is destroyed are only triggered when the last model that started the battle in an attached unit is destroyed.
An attached unit has all of the keywords of all of its component units. As such, an attached unit is affected by any rule that applies to units with any of those keywords. Note that models in an attached unit do not gain the keywords of other models in that unit that they do not already have. Remember that attacks target units, not models. Example: An attached unit contains a leader model with the PSYKER keyword. While that model is part of that unit, that unit has the PSYKER keyword, even if the bodyguard models do not have that keyword. If that unit is attacked by a weapon with the [ANTI‑PSYKER 4+] ability, any unmodified wound roll of 4+ made against that unit is a critical wound, even if the attack itself is not allocated to that leader model.
Abilities/rules that affect a single specified model (e.g. from an enhancement or an item of wargear) only ever apply to that model, even while part of an attached unit. Otherwise, abilities/rules that affect a unit (or models in it) apply to every model in an attached unit, until the source of that ability/rule is destroyed, as shown below. ABILITIES IN ATTACHED UNITS SOURCE OF ABILITY/RULE APPLIES TO THE ATTACHED UNIT UNTIL The last model in that leader/support Leader/support unit unit is destroyed.* Bodyguard unit The last model in that bodyguard unit (e.g. from a datasheet ability) is destroyed. A specific model (e.g. the bearer of an That model is destroyed. enhancement or an item of wargear) * This means leader/support units continue to benefit from their own ‘while this model is leading a unit’ abilities even after their bodygu unit is destroyed, provided they started the battle in an attached unit In all of the above cases, if that last model was destroyed as the result of an attack, the ability it was conferring upon the attached unit applies until the attacking unit has resolved all of its attacks. ITS STRATEGIC RESERVES Strategic reserves are units that arrive on the battlefield at different times, ADVANCED either because they were held back during deployment, or because they are using special abilities to reposition themselves.