They call out left or right as they see them.

The angle of the left and right tombstone makes this side visible to the middle plate holder, so they should be the person who looking to see what's lit. The side facing the Warpriest on one of the tombstones will light up, but will only be visible to people standing on a plate. After defeating three Revenant Knights that zone in on the three plates, a 'Glyph sequence' is started.The person assigned to middle plate must stand on it, and look at the three tall Tombstones, then step off of their plate.

When the fight begins, adds fill the hall: Acolytes, Adepts, Knights, Wizards and Thrall. To learn more about this Destiny 2 raid, visit our King's Fall walkthrough hub.

You do, however, need to designate at least one person to the left, middle and right as you enter the Warpriest's hall, where they'll initiate proceedings by stepping onto three activation plates. Responsibility for damage is shared across your entire team. Warpriest is the first boss of King's Fall, coming shortly after Basilica, Annihilator Totems and Deathsinger's Power, and the first major DPS test in this Destiny 2 raid.

Warpriest raid: shadow legends reddit