So I've been carrying around a "Relic Coffer Key" that was dropped off a
mob in BRD. Didn't know what it was for and was annoyed that it was taking
up space in my bag.

Last weekend I found out firsthand why I've been carrying it around. I was
invited by real-life friends who are in the Prophecy of Ascension guild
(hereafter "PoA" for brevity) to a 10-man raid of BRD for the specific
reason of farming the "Vault" room. For anyone who doesn't know (I
didn't), the "vault" is a room off the exit corridor from the arena. In
it, there are about 12 locked doors that the Relic Coffer Key will open.
There is one locked door in the back center of the room that the relic key
will not open. This middle door is why PoA goes there. In the chest
behind the middle door, 50% of the time, the loot is "Burning Essence."
Each of the other vault doors has a chest in it with some loot (the best of
it is usually green, mostly it's junk).

PoA farms burning essence because it's an ingredient in the Libram of
Resilience quest. The Libram of Resilience, when completed, adds +20 fire
resistance to a helmet or leggings (two armor pieces that generally don't
allow enchants). If you do it twice, you can have it on both. From what
I understand, fire resistance is critical to success in defeating the MC
and BWL bosses, moreso even than armor for non-tanking raid members, who
usually only suffer AoE damage. I'm told that there are members of PoA
whose fire resistence is nearly 300, unbuffed. During boss fights, their
health level barely moves.

The Libram of Resilience +20 fire resist has, I think, the following ingredients:
1 Burning essence
1 Black Diamond
4 Crystal Spires (a reward from a repeatable UnGoro Crater quest)

We farmed the vault room four times in a little over an hour. This is how
it typically goes....

1. Raid group forms at the instance for buffs, etc..
2. Fight your way up to and through the arena (mainly to pacify the
spectators).
3. Go upstairs to where the spectators are and kill a specific dwarf
sitting on a bench. He carries the key to the center vault.
4. Run to the vault room and open all doors but one. Opening the last door
activates the golems.
5. Once all vaults have been emptied and the party is ready, open the last
vault, fight and kill golems and a dwarf that comes. The fight is easy in
a 10-man group. The whole fight takes less than a minute.
6. Run out of the instance, disband the raid party to reset the instance,
reform raid party, rinse, repeat...

Librams of Resilience sell in AH for about 20-25g. Black diamonds usually
go for between 8g-15g. The spires are free if you do the quest in UnGoro.
And in the four raids on the BRD vault, burning essence dropped twice
(which confirmed the reported 50% drop rate).

While it may seem like grunt work to do this over and over again, I see it
as critical to having any kind of success against mobs that use fire, which
is virtually every boss in all of BRD. PoA does this during MC down time,
while they wait the 4 days for the instance to reset. Seems like a good
way to spend down time (when not helping other guildies power-level). I
have had plenty of evenings where I stared blank-faced at my computer
trying to decide what to do when not raiding something. What's nice is
that it's an easy 10-man raid, so we should be able to do this "all guild"
no problem.