Does this thing even drop? I need one of these to craft a caster armor and I’ve been farming possessed arcanists/archmages for hours and still haven’t seen a single one drop. The drop rate is way too low.
Maybe from the ‘Ascended’ enemies in Cronley’s Hideout?
Just a guess…never needed one
I think those don’t drop caster armor pieces. The painful thing about farming this thing is that the possessed arcanists/elementalists/archmages are already rare mobs to begin with, and on top of that I need them to spawn as elites to even have a chance at getting one to drop a green robe. I’ve had them drop a whole bunch of ascended epaulets and diadems though, just not the chest armor…
I guess I’m giving up. By the time that darn thing finally drops I’ll probably have reached lvl 85. It really sucks though because I need that blasted thing to craft an armor that’s part of my set.
Drops from the possessed mages etc in Aetherial areas, namely The Gruesome Harvest, Plains of Strife etc.
You’re extremely unluccky if those never dropped for you. i’m wearing those rover on my character cause they rolled good stats.
Ascended pieces drop from every second one literally
Like I mentioned before I kept getting either Ascended Epaulets or Ascended Diadem from those mobs, just not Ascended Vestment. It’s probably a curse or something lol. Either of you above happen to have a spare one lying around? Perhaps you’ll be willing to trade and help a brother out? 
I just got the Ascended Vestments on my fourth run on Plains of Strife. I can also say that it’s a good place to farm them. You just go to Gates of necropolis rift and go back on the Plains, killing each Arcanist you find. I did it on Elite and there were 3 or more arcanist heroes on every run, but in the end the one who droped Ascended Vestments (not Haunted Vestments nor Ascended Robes) was a white arcanist I killed.
I’m having the same problem, lots of pauldrons and diadems, no vestments. I’m doing it at lvl 85 on ultimate, do they drop more frequently at lower levels?
It’s pure rng I believe, and probably not very fair too. Rare ascended shoulder and head slots definitely have a much higher chance to drop than chest.
If I remember correctly I finally got mine from a normal arcanist mob (not even a hero mob) in the necropolis after having obtained like 15 of those shoulders and diadems.