Strike from the Stars: A subtle shifting of the heavens is the only warning of a Shadowstrike Starhost assault.
Instead of setting up a unit from this battalion on the battlefield, you can place it to one side and say that it is waiting in the stars as a reserve
unit. At the end of any of your movement phases
, you can set up any of those units on the battlefield more than 9" from any enemy units. Reserve units that are not set up on the battlefield before the start of the fourth battle round are slain.