The Behemoth is a boss from Final Fantasy II, first encountered when Firion and his party, along with Gordon, enter the Palamecian Coliseum in order to rescue the abducted Princess Hilda. They realize too late that it is a trap, and the Behemoth is unleashed on the heroes.
The Behemoth is a deadly foe, but a much simpler fight than the Lamia Queen, which precedes it. He does not use any status-effecting spells, but prefers heavy brute force, which is backed by an impressive Attack stat. He also boasts high HP and Defense stats, which tend to lengthen the fight. Defeating him is very straightforward, just hack away at his HP with your strongest melee characters, and have your mages bombard him with high-level black magic, pausing to heal injured comrades as necessary. With its eventual defeat, the party will gain access to the Coliseum's dungeon, from which Princess Hilda may be rescued. The Behemoth can also be fought in the forests near Mysidia, making it a very unfortunate find for those trying to journey to Mysidia early in the game in hopes of obtaining better equipment, weapons, etc.