A BCNM (or Burning Circle Notorious Monster). These are obtained by trading an orb to one of the three Burning Circle's in the beastmen area's of Vana'Diel. You can obtain an orb by trading your beastmen seals (bet ya been wonderin what to do with those eh?) for them in Jeuno. You can trade 40, 50 or 60 seals and receive, in return, a lvl 40, 50 or 60 orb (depending on amount of seals respectively). These BCNM's have some extremely rare drops that can only be obtained by defeating them. Of course, as you guessed it, these are no forest hare's and tiny mandagora's... in most (if not all) occasions, a party would be required (or at least recommended if you're cocky and stubborn).