Ghazkulls Waaagh! can be summoned at any time, but only once per game, and not in the first game turn. It replaces the army's usual Waaagh" - the one is better.
Ghazkull's Waaagh! lasts the remainder of that player turn and all the following player turn. During this perios, Ghazkulls saving throws are invulnerable.
Furthermore, for the
duration of the Waaagh! all Ork infantry units
automatically count as rolling a 6 for their Run
distance. All non-fleeing friendly units become Fearless for the duration of the Waaagh!
Note that no more than one Waaagh! can be called per turn, so Ghazkull connot combine his Waaagh! with the Waaagh! generated by a Weirdboy.