New Necrons vs. Dark Eldar FEAR THE REAPER 1850p BATREP

Today, we played the Haemonculus Covens mission Fear The Reaper with Covens going against the Necron Decurian Detachment...

Here´s the info :

"No Objective Markers are set up at the start of the battle. Instead, each time a unit from the enemy player’s army is completely destroyed, an Objective Marker is placed by the enemy player within 1" of the location occupied by the last
model from the destroyed unit to be removed as a casualty (but not in impassable terrain). The normal restrictions that apply to
placing Objective Markers are not used in this mission, which can result in an Objective Marker being placed within 6" of a table
edge or 12" of another Objective Marker. Note that only units from the enemy player’s army generate Objective Markers; units
from the Haemonculus Covens player’s army do not.
First Blood, Line Breaker, Slay the Warlord"

It uses the Vanguard Strike and you choose the sides normally and who deploys first, BUT the Dark Eldar Covens decides, if he goes first or second. You can try to seize the initiative...