I'm still trying to figure out what the big issue people have with getting this lovely(Yes, I refered to it as 'lovely') little key is. It could just be my Treasure Hunter kicking in from /THF, but I get it in 5-10 mobs everytime I run up for it solo. I normally go fetch a key and farm the Yagudo on the lower levels for necklaces while I keep an eye out for the chests to pop. I have more trouble with the chests being illusions than getting the keys to drop.
For a bit more reference, I saw about 10 of these things drop in a 2-3 hour period. Was duoing with an LS buddy of mine in the last room. We chained 3 and 4 at a time and sometimes got 2 drops off one chain. Neither of us had Treasure Hunter at the time. Was DNC/MNK(me) and PUP/WAR(Kildabeasttwo- a.k.a the craziest Elvaan you will ever meet ;p) synced to my 23, then 24 once I leveled. The key mobs were easy kills as long as they didn't chain when we had low hp and no Trance to back the two of us out of it when we got caught up chatin'. o0;
Keep Silence on the Theologists and Priests(if you have it-not too bad if you don't), and just beat the crap out of the Votaries if you are soloing. Easy as cake. :3 You should see one drop fairly quickly.
>< I said my 2 cents and wrote a speech, sorry, hope my words help though. Need help getting one on Fairy with in the next few days to a week, /tell Kiayashi ingame and if I am online, I will help you, as I will probably be running trips to Giddeus for necklaces my entire time online... Don't you just love Norg Fame quests??