In Final Fantasy XI there's one boss that "stands above all" which is the Pandemonium Warden. A guild by the name of BeyondTheLimitation formed a raid and attempted to defeat said foe and spent over 18 hours on "it". Apparently the boss change forms and after twenty times of changing the guild simply gave up. Raiding for 18 hours without a break isn't exactly very healthy. It gets even better though, according to FFXI's very own warning's message, it states:
Exploring Vana'diel is a thrilling experience. During your time here, you will be able to talk, join, and adventure with many other individuals in an experience that is unique to online games. That being said, we have no desire to see your real life suffer as a consequence. Don't forget your family, your friends, your school, or your work.
This is amusing, since it does not mention your health in it.