GLITCHED - One of the Collective members can despawn, making this trophy impossible on your current save, see below for more details.

The Idols Collective are the leaders of the Idols and you must kill all six for this trophy. They are stronger enemies with LED helmets. They are found as follows:

The one that can glitch is the threat one. I'd recommend making a manual save before placing a venture in Old Town West, when you do go around and complete them, and if you finish the one that asks you to defeat the collective member without actually killing him (this seemingly happens if you kill too many of the goons), reload your save. If you've already ran into this issue and don't have a save from beforehand, you can join a co-op partner that has this threat incomplete and kill the collective member there, or you'll have to start a new save and complete most of the story again to get this trophy.