Last week our guild (myself included) got the "Glory of the Firelands Raider" achievement. With it came a shiny new firebird mount and some bragging rights.
It's "kind of" a big deal in the sense that we're maybe like the 10th guild on the server to get this. There are other guilds who have the same boss kill progression who haven't done the Glory meta achievement yet
This is also the first Glory meta mount I've earned in a relevant tier of raiding. In fact, the only other meta mount I have from raiding is the ICC frostbrood drake, which I didn't get until a couple weeks into cataclysm.
The thing about these metas is that it's possible to get about half of them just by sheer luck. The other half require you to do something outrageous that you would never think to do in a normal raid.
For instance the Baleroc meta achievement requires that no one gets the Tormented debuff more than 3 times. This is very easily doable with high DPS without even trying for it. The Rhyolith achievement requires that you only turn in one direction, which is also possible to do without trying (although random volcano placement makes it unlikely).
But then you have things like Bucket List, which requires you to drag Shannox to all corners of the map before killing him. Why on earth would you intentionally do that?
The achievement that we really had a hard time with was Alysrazor's: Do a Barrel Roll. It required that no one in the raid group gets hit with 4 different abilities. Of them 3 are very easily avoidable if people are focused and getting interrupts out correctly, but the last fire attack, the tornado, is what had us banging our heads against the wall for two nights.
It really should've been an individual achievement and not a raid-wide one. Do you know how hard it is to get 10 people to execute this perfectly at the SAME TIME? I admit there were a few people who did it time after time and never got hit once, but inevitably the other half of the raid kept messing up (myself included). It doesn't matter that I did it perfectly 4 times in a row - if I'm the only one who messes up the 5th time, BAM there goes the achievement.
Finally, though, after all the practice we were able to manage it somehow. I pray that I never ever have to do that again.
My guild and I have done some ridiculous things in the name of achievements. Iron Dwarf, medium rare is probably one of the most ridiculous in that it forced us to all gimp our DPS severely, taking care to get the adds' HP down low but not too low, then sit around for 10 minutes doing nothing. Usually after that we had to force a wipe and do it a couple more times so we could get the 25 required kills (you could only do 10-15 before she enrages).
Full House in ICC was also a total clusterF. Normally you want to KILL the adds, not let them run around like crazy going apeshit. The problem was actually that the adds would keep dying from the tanks' autoattack. Finally we had to resort to making the tanks drag the adds far enough away and just sitting there, getting beat on but not attacking.
The most insane one was probably the LK achievement which required you to stack the debuff up to 30 before phase 2. The difficulty of it was the sheer RNG and quick reaction time required. Basically all the DPS had to sit around for about 20 minutes (literally) twiddling their thumbs, unless they got the plague in which case they had to make a mad dash to go stack it on the ghouls. The toughest part was not zoning out and staying alert enough to do this simple action. Not a very difficult achievement in terms of skill, but man, it was ridiculous how hard it was to get that to 30. It would keep falling off at 20, 25 and people would just want to rip out their hair.
The achievement that will forever elude me, I think, is the Safety Dance. I've tried that in multiple PuGs that were wayyyyy overgeared for Naxx, and people still get hit by that stupid poison. There's probably a way to cheese it so that nobody gets hit but to do it the proper way requires way more focus than a typical PuG can provide.
I still have a bunch of 10 man Naxx/Ulduar ones I'd like to do at some point. I haven't even touched the majority of ToC. The content is just difficult enough that I'd need at least a 5 man group or something to try it, and it's not easy getting people to come help you out for no significant reason other than nerd points...
Maybe I can solo all of it when I'm level 90. Maybe.