Champion of Ulduar

Note a significant difference in this undying compared to the Naxx undying - there is no stipulation that it must be done within one lockout. So the achievement can be done over multiple weeks of raiding. However the kill must be the first attempt for that week's raid if you wipe and then have a perfect kill it does not count.

edit: Also interesting is that Algalon the Observer is not on the list.

Tried it last night and it is completely gone. Had missed only General Vezax from the night before the patch (stupid dps not watching aggro) got him down last night flawlessly and still did not get the achievement. Hope this clears up the confusion cause we were hoping the FoS didn't mean it was unobtainable but much to my despair it is. =(

Algalon the Observer has his own, for some reason. I guess he's just that difficult.