Tarasque

Tarasque is a level 200 dragon monster that will need at least two teams of level 200+ players to kill(one with Shadowlands). He is found in camelot castle. If you fall into the lava pool in his lair, you won't die but lose some health.

The dragon in particular takes more then a single group to take down, and is a very hard fight for the unprepared. He will also not leave his room, so is impossible to pull out into any larger area.