WoWDB

This achievement is part of the Firelands meta achievement  that rewards a Corrupted Firehawk.

[Only the Penitent...] is really simple as far as what you have to do, but also very easy to screw up.  Not only is it picky about how it is completed, sometimes it seems flat-out bugged; I've seen fails when it seems like everyone does everything perfectly.  I highly recommend downloading an addon that monitors achievement failures for this one.

So, start-to-finish instructions:

Introducing Majordomo Fandral Staghelm & Friends


This achievement requires six people regardless of raid size.  Split into two reliable groups of three - with one group going for the left orb and the other group going for the right one. The remaining people will wait by the portal where it is safe; they will still get credit.  You will not be required to kill the boss to complete it.

Staghelm chain casts something called [Kneel To The Flame]. When the cast time finishes (it is several seconds long), there is an AoE explosion to everyone in his room who is standing or mounted. The way to avoid damage, and thus earn the achievement, is either be sitting or kneeling when the cast finishes.  Everyone should run during his cast.  When his cast is about half finished, sit down and wait until the AoE goes out before standing and running again. I highly recommend playing it safe and sitting early rather than at the last second.   You can use a /sit or /kneel macro, or you can just hit 'X' (which is the default keybind if you haven't rebound it).  Test your keybinds and macros before you start running.  If anyone takes damage from his ability, the entire raid has failed.

Ways To Mess Up Running To The Orbs:
• Combat pets take damage from his explosion and cannot sit, so dismiss them before running.
• You'll fail the achievement if mounted.  Dismount.
• Do not use bubble, cloak, ice block, and other invulnerability abilities through his casts.  You must be sitting or kneeling.

Once you get there, you will find that in front of each orb are three swirlie orange things. When each person arrives in front of the orb, they should sit on one while they wait for the others.  You do not HAVE to be sitting on these for it to work, but they are a good indicator that everyone is in place and close enough to get that magical golden cog without having to adjust positioning when the time comes, so I recommend actually sitting on them.

Once everyone is sitting on the little orange swirlie seats in front of the orb, have everyone hover their cursor over the orb and make sure the cog is golden (but don't click yet!).   While everyone remains seated, have someone count down a pre-determined number of casts, preferably on voice chat. I recommend setting a number ("Click in three more casts... 3... 2... 1-click") rather than just shouting to click since latency can mess the group's timing up.   As soon as the agreed number of casts finishes, all six people will simultaneously single click the orb in front of them.  If anyone accidentally starts early or misses the click, you can't cancel your channels and try again.

More Things That Can Bug The Achievement
• Do not be in any shapeshift (druid, shaman, etc) forms, or in a costume/disguise.  Worgen form is okay.
• Do NOT click the orb more than once.
• Try not to click too much earlier or later than everyone else.
• Do not stand/jump, then click. Just click from sitting and let your character stand up automatically.
• Do not cancel the channel once it begins.  Stand still.

Your click will start a channeled spell to the orb. At this point, if everyone did it right, achievement credit will be given and the orbs will despawn. If you messed up, the orbs will despawn without credit.  

You can all leave the instance and reset it and try again, but you are still bound by the instance limitation and can only try five times in an hour.  Additionally, we had trouble getting the achievement to reset, so I recommend resetting it by having the entire raid run outside the instance, removing the person who caused the fail, resetting, entering inside, then reinviting that person and having them enter last.