From Lylat Wiki, your source on Star Fox information. By Fans, for Fans.
Mechbeth is a mechanical construct used in the defense of Macbeth during the Lylat Wars in Star Fox 64. Created by Andross, Mechbeth was an advanced combat system with a fatal flaw: its internal power generator was still in development at the outbreak of the war. For this reason, it had to rely on an outside source for power, tethered to an energy supply train. However, its combat computer was fully functional. Mechbeth was also armed with three potentially dangerous attacks: an explosive iron bar launcher installed on the head, beam generators installed on the wings, and a tail in which it can spear its enemies and drop them. These three attacks were purported to be the most deadly weapons ever designed on the planet.
Mechbeth can be defeated using one of two ways, and the method used will ultimately determine which stage the player is able to visit next. The first method is simply to fight it head-on. Mechbeth's weak points are its "head" with which it fires its lance-like projectiles, and its "mouth" which it uses to scoop up and bite the Fox's Landmaster. Once those have been destroyed, a hatch will periodically open on the train and drop boxes which project energy barriers; shooting inside the opening will cause Mechbeth to spin wildly out of control for a few seconds, exposing its vulnerable back, which must be shot in order to destroy it. If this method is used, the player will take the "easy" path to Bolse.
If the train reaches the supply depot during this fight, he'll have the weapon use an instant kill attack on Fox.
The second method is the preferred method, and is arguably easier, though planning is required, and that is to switch the track by shooting eight tall switches by the side of the track. Falco will shoot the eighth switch if he is present, and if the player came to Macbeth from Zoness, Katt Monroe will shoot the second and fifth switches. Once all eight switches have been hit, the large switcher lever will appear which will switch the track when shot, causing the train to crash into the fuel depot, scoring a Hit+50. If this method is used, the player is able to choose to take the "hard" path to Area 6.