Empyric Castellan

Once per battle, at the start of any phase, this unit can use this ability. If it does, until the start of your next turn, this model has the following ability:

Empyric Castellan (Aura, Psychic): While an Adeptus Astartes unit from your army is within 6" of this model, models in that unit have a 4+ invulnerable save.