Master of the Dark City
Codex: Dark Eldar, p. 18
If this unit is in your army and your Warlord, when determining who will take the first turn, you may roll 2D6 and take the highest result. At the start of the First Battle round, before the first turn begins, if you are going second, before the first turn begins, you may roll 2D6. If either dice is a 5 or 6, you may take the first turn instead.