Hah! Finally a design for this massive machine I can live with.

Behold, the Mechapede!

(Warning: Those of you who hate bugs and things with multiple legs, this thing is a mile long...RUN!!!!)

When the Collective advances on a planet, usually the last step in rooting out any rebellious organics is sending in this monster, a Class C World Eater Drone, otherwise known as a Mechapede. The only one in existence, this monstrous automaton burrows through a victim planets crust, using sonar waves and its own visual scanning to detect urban locales, such as cities and towns, forts and even underground bases. From there the Mechapede will instill chaos by strategically digging just under the city's foundation, literally sinking it within hours of burrowing. The Mechapede will gladly devour metal, cement, rock, water, soil, even entire buildings and their foundations, it's hunger knows no bounds. It retains its ability to constantly eat by processing the bits and pieces it has eaten inside of itself, grinding it all down and sometimes disintegrating the material, dumping whatever it cannot "digest".

The Mechapede is an extremely large and very powerful machine, but like any machine, has its own weaknesses. Its armor plates can withstand the burden of burrowing through solid rock, so it can easily repel attacks from tanks and the like. It is unknown if Mechapedes descend to a planet's core if at all, this tactic being very detrimental to the only one in existence. The Mechapede avoids areas too hot or too cold (by definition hot being pure magma or the center of a planet, cold being temperatures colder than the vacuum of space itself), and it is smart enough to know when to stop digging.

The Mechapede is a sentient machine, and it is unknown how the Collective could assemble something so massive and give it the ability to think on its own. It's personality is destructive and single minded, but it seems to take enjoyment on periodically surfacing and instilling bone chilling fear into its enemies before devouring them whole. As of the invasion of Earth, the Mechapede was already deployed to the Moon to destroy the UNMD outposts, with the machine quickly destroying the bases and nearly itself when the Moon began to destabilize and break apart from the excessive burrowing. Eventually the Collective managed to retrieve Mechapede before the Moon completely broke apart in space, its pieces scattering across the solar system.

The Collective eventually deployed the machine to Earth, but kept it dormant during most conflicts. It is believed to be underneath a large ice shelf in Antarctica hundreds of feet under the ocean, waiting for its masters to reactivate it.

This drawing was based off of a picture of a Metal Head I found from Google...I needed a muse and I finally found one...so here it is :3

Scary ain't it?