It just got ridiculously more stupid. Apparently the newest top tier boss to defeat could take over 24 full hours of fighting to actually take down. I checked on an old livejournal this morning that I used to track when I was really into FFXI (this guy is in the best FFXI guild there is) and he had 2 big updates about Pandemonium Warden, the hardest boss in FFXI yet, apparently.
The boss shapeshifts into the form of every boss that has ever existed in the game up to this point, and you have to defeat each one before he turns into another one. This guild fought PW for over EIGHTEEN HOURS before they just had to stop, people were passing out from exhaustion, some were getting physically ill, like jesus christ Square, 18 hours on a boss fight? I'm so glad I quit that game.
EDIT: Also to add, they went through 20 forms up to this point and they estimated it'd be at least 5 more hours before they could down him, assuming there were no more forms left.