Keeper of Petition
From Destinypedia, the Destiny wiki
During the Vorgeth encounter players must immediately kill the Keepers of Petition scattered around the arena in order for them to drop an orb with the "Petitioner's Mark" debuff in it that lasts 45 seconds. The Keepers' debuff needs to be stacked four times and dunked into a plate in the arena in order to damage Vorgeth.
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