I remember in the past doing the som quest relatively easily. Now, I have gotten the crooked staff and the serpent scale but am unable to find the minion that used to be in elven caves. I also was quite shocked to find a bunch of new mobs in the elven caves that dropped strange polluted junk.
Is there any use for this stuff and where is this elusive dark elf?

The elusive minion you are
The elusive minion you are looking for spawns about every hour, but, for whatever reason, bots tend to end it quickly. I spent about two weeks hunting Elven Caves for the minion.
As for the polluted stuff, I believe that is part of an elven quest.
Yes. The pulluted stuff
Yes. The pulluted stuff that you refer to is part of the Named Set for elves
http://lineagedb.com/quest/detail.php?id=41&sg=1
The minion is hard to find. One of my mages has the same items you have. I can't find the minion to turn it in. qq
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Well, before the elf caves
Well, before the elf caves update I used to hunt there for rough now and then and there were usually 2 or 3 minions up all the time, since that update though I don't hunt there but have tried finding the minion a few times and it is very rare.
There was obviously a hidden update when this elf caves change came in that decreased the spawn of minion, I have done this quest a number of times before and after the update that resulted in the minion going from the easiest elindaire component piece to get(BY FAR) to the hardest piece to get.
It does still spawn there though