Broodcoven

The three models of a Broodcoven must be deployed as a single unit. They can still join friendly units, but if one does so, all other Broodcoven models must join the same unit. Similarly, if one Broodcoven models leaves a unit, all other Broodcoven models must also leave that unit and they must form back into a new unit composed of Independent Characters again.

The Broodcoven unit and any unit they join have the following special rules whilst the relevant model from this Formation is still alive.
Patriarch: Fleet
Magus: Counter-attack
Primus: Preferred Enemy