While a Bodyguard unit contains a Leader, it is known as an Attached unit and, with the exception of rules that are triggered when units are destroyed (pg 12), it is treated as a single unit for all rules purposes. Each time an attack targets an Attached unit, until the attacking unit has resolved all of its attacks, you must use the Toughness characteristic of the Bodyguard models in that unit, even if a Leader in that unit has a different Toughness characteristic. Each time an attack successfully wounds an Attached unit, that attack cannot be allocated to a Character model in that unit, even if that Character model has lost one or more wounds or has already had attacks allocated to it this phase. As soon as the last Bodyguard model in an Attached unit has been destroyed, any attacks made against that unit that have yet to be allocated can then be allocated to Character models in that unit.

Each time the last model in a Bodyguard unit is destroyed, each CHARACTER unit that is part of that Attached unit becomes a separate unit, with its original Starting Strength. If this happens as the result of an attack, they become separate units after the attacking unit has resolved all of its attacks. 

Each time the last model in a CHARACTER unit that is attached to a Bodyguard unit is destroyed and there is not another CHARACTER unit attached, that Attached unit’s Bodyguard unit becomes a separate unit, with its original Starting Strength. If this happens as the result of an attack, they become separate units after the attacking unit has resolved all of its attacks. 

Each time a unit that is part of an Attached unit is destroyed, it does not have the keywords of any other units that make up that Attached unit (unless it has those keywords on its own datasheet) for the purposes of any rules that would be triggered when that unit is destroyed.

Oath of Moment

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.

Profiles:

Abilities
Vengeance of the Omnissiah: If a friendly ADEPTUS ASTARTES VEHICLE model is destroyed within 12" of this model, until the end of the battle, this model’s Iron Priest hammer has an Attacks characteristic of 6.
Leader: This model can be attached to the following units: ■ Thunderwolf Cavalry
Iron Priest: While this model is within 3" of one or more friendly ADEPTUS ASTARTES VEHICLE units, this model has the Lone Operative ability
Blessing of the Omnissiah: In your Command phase, you can select one friendly ADEPTUS ASTARTES VEHICLE model within 3" of this model. That model regains up to D3 lost wounds and, until the start of your next Command phase, each time that VEHICLE model makes an attack, add 1 to the Hit roll. Each model can only be selected for this ability once per turn.

Unit	M	T	SV	W	LD	OC
Iron Priest on Thunderwolf	10"	6	2+	5	6+	2

Modifiers:

append name (Battle-hardened)

and

16+ selections of Experience Points in self (recursive)

30- selections of Experience Points in self (recursive)