Tyrant Guard Brood

If a Hive Tyrant is killed whilst part of a unit of Tyrant Guard, the surviving Tyrant Guard immediately gain the Furious Charge and Rage special rules. These abilities last for the remainder of the battle.

A single Hive Tyrant (including the Swarmlord) may join a unit of Tyrant Guard exactly as if it were an independent character. If a Hive Tyrant (or the Swarmlord) has joined a unit of Tyrant Guard, the unit cannot go to ground, voluntarily or otherwise.

see Instinctive Behaviour

A unit that Feeds is subject to Rage. In addition, the unit may not fire any weapons in the Shooting phase, though it may still run, according to the stipulations of Rage.