Take down the Behemoth is a mission in The Lost Frontier. After defeating and pursuing Skyheed, Jak returns to the Phantom Blade to prepare for the final fight against the Aeropans's leader, who has retreated onto his ACS Behemoth.
The fight begins with the Behemoth encased in a massive dark eco shield, which is promptly taken down by a missile volley from the Phantom Blade. You must then destroy the large dark eco crystals that jut out from the sides of the ship's hull near the front, which is relatively easy as the majority of the ship's turrets are near the wings and the rear. After both crystals have been destroyed, six heavy fighters, each accompanied by two fighters, will take off. You must now destroy all of the Aeropan planes, during which the Behemoth restores its shields.
After all heavy fighters and fighters have been shot down, the pirate galleon will launch another volley of missiles, where after you must destroy another pair of crystals, this time next to each wing. Periodically, the Behemoth may launch a defense rocket (identical to the one Daxter had to comandeer during the mission "Bring coordinate sphere back to the galleon"), which will put you in the point-of-view of the rocket while you must steer your ship away from it. After this, the ship launches more heavy fighters and fighters. The Behemoth will, after its shield has been destroyed a third time, now reveal a pair of crystals on the wings as well as a new defense system. Said defense system involves a group of eight drones projecting a large force field, destroy the field and each drone as they will follow you and prevent you from targeting the ship. As you target the crystals after taking care of the drones, beware of the nearby turrets protecting them.
After taking care of the third set of Aeropan planes you must destroy the final dark eco crystal on top of the rear of the ship. Said crystal is heavily guarded and will periodically release a large pulsing mass of dark eco, which will engulf your ship and trust you into a short tunnel filled with hazardous blobs of dark eco. Dodge them and then proceed to continue targeting the crystal until it retaliates, destroying your ship in a cutscene, during which Keira rescues you in the Hellcat and Phoenix sacrifices himself along with his pirate galleon.
The Hellcat will now be equipped with Keira's newest weapon, an overpowered laser beam. Use it to cut through the few planes that appear, along with the last four eco crystals, one of which is positioned on the nose of the ship, two on the back of each wing, and the final on the rear of the ship, guarded by another set of drones projecting a force field. Once all crystals have been destroy the Behemoth will fall apart and explode, finally putting an end to Skyheed and the Aeropans.