Carved from the horn of a slain rival, the clarion call of a brayhorn is a chieftain’s summons to any Beastmen who hear it.
From the beginning of round 2 onwards, if your General is on the battlefield during the Command sub-phase of their turn, they may attempt to sound the Brayhorn by making a Leadership test. If this test is passed, you may immediately roll again for each unit of Ambushers in the army that is held in reserve and that did not arrive during the Start of Turn sub-phase of this turn.
Note that this special rule may only be used by a Beastlord or Wargor that has been selected to be the General of the army.