SubDesert Core

Zero can pull the four blue plugs under it with the Zero Knuckle to deactivate the large laser attack. Alternately, one can also use the weapon obtained from boxes earlier in the stage to deplete his energy quickly.
 * SubDesert Core (サブデザート・コア), shortened Sub Core outside Japan, is the first boss of Mega Man Zero 4, the core of a desert vehicle similar to a submarine.It attacks with giant lasers and small energy spheres, and BeamWalkers appear to help it.

Trivia
It bears a slight resemblence to the Pantheon Core of the first Mega Man Zero game, and the Shiriko da Gama from Mega Man 8.