Slay the ferocious Darkmoon Rabbit.
This is an NPC is an homage to Monty Python's Quest for the Holy Grail. He has 174million health points and is found in a cave on Darkmoon island during the week DMF is occuring. He is very tough for his cute, furry appearance. Killing him rewards the achievement [That Rabbit's Dynamite!]. He drops one Darkmoon Rabbit pet per raid.Have everyone stand in the back of the cave for the start. He is neutral and will not automatically aggro, so you should be able to walk right past him to the back.I recommend a full raid to kill him, although I would not bother with a balanced raid comp - just grab as many people as you can. With regards to DPS, ranged DPS will have a much, much easier time than melee. Although he randomly attacks raid members, it appears he can be tanked between attacks, so a couple tanks probably won't hurt.The rabbit will latch onto raid members with his ability [HUGE, SHARP TEETH!], causing you to flee in terror (and probably die).The key to beating him is making sure that raid members are good about running back as soon as they die. Do not let people sit on the floor dead (unless they are waiting on a rez timer), because he will pick through your raid and you need enough people cycling alive to prevent a total wipe and reset. That's the key to beating it; make sure there are always people alive. It will take awhile, but eventually the live people will whittle him down while the dead people rez and take turns. You might not need a full forty man raid, but the more the better, so I would get as close to full as possible. We had a forty plus a couple people standing around helping.The reason to start in the cave is that if a player runs into the water or too far from the cave, he can reset. So make sure everyone understands to stay in that cave! If you get feared out, run back in, all the way to the back, as soon as they are free, and make sure that you rez inside. It also makes it harder for other people to grief you by force resetting him.
update: at level 90, you can probably get by with far less people than you needed at 85.