There are 5 of this mob in Ikky Transcendence. One in the first room on the right where the single Priest of Righteousness was in Ikky 1. One in the first room on the left between the two cubbies where the two PoR's were in Ikky 1. And three in the backwards E room, one behind each altar (in each cubby). These three you can kill in their cubbies without aggroing the next one over.
Otherwise they're pretty much like the Priests: they enrage, infuriate (ramp and flurry? not sure), don't have a lot of HP's, and are leashed. Each one drops 1 of 5 pieces to create the key to the Guardian's final room. For us, the final Acolyte we killed (the southernmost one) dropped two pieces of loot (mantle of mending and bloodlink chestmail).