From Destinypedia, the Destiny wiki
In the Gauntlet and Throne encounter of the Leviathan, the Psionic Projections act virtually the same but are used in different ways. In the Gauntlet encounter, when a Psion Councilor isn't killed in a certain amount of time it will summon in one of these projections and will continue to flood the area with more projections the longer it stays alive. If the Psion Projections themselves are not killed they will initiate the Mental Collapse wipe mechanic, killing the entire team. This mechanic is used again by the Projections within the Throne encounter in which they only appear in the Nightmare Realm portion. Like the Gauntlet, if the Psionic Projections are not killed, they will activate their Mental Collapse, wiping the team.