How about a big vat of flaming grease for them to fall into?

Kills zombies, AND provides a food supply! BRILLIANT!

Fried rotten meat doesn't sound very appetizing...

Hmmm... How about A Automated mobile mine, Gathering resources to fuel its Also automated factory which produces ammo for the automated Gun cannons? The Vehicle is powered by solar, and at night off geothermal power from a drill attached to the mining equipment. Dare I say the ultimate invention for a war against Zombies?

Mining is a slow, lengthy process. There's no way in hell that would be feasible. Though you could get away with a quarry excavator, those things are so ♥♥♥♥ huge that you'd be safe from anything that's not airborne.

Lubricate the death machine with zombie blood. Duh.

How about a mantle Fluid extractor ( Probebly even Worse)? If the problem of cooling comes along, a (solar PowereD) Atmospheric compressor to create liquid nitrogen to cool the devices... Problem is I have no idea how to purify fluid.

A mantle what now??? And... purification? Excuse me? Why the bloody hell would magma require filtration?

i think he means the liquid nitrogen.

FUH-FUH-FUH-FACEPALM.

Though that would work, how would you practically be able to pull it off?

How the ♥♥♥♥ would a mobile drill capable of digging through several kilometers of rock be useful against zombies? You'd waste a fairly large part of what you dig up just to make new drill bits, which break with alarming frequency when digging that deep.

How in god's name would you even transport it? The shaft of the thing would need to be massive, even if it was a floppy snake drill or something. There are also just much better ways of getting power.

I'm still stuck on why he'd want purified mantle and how he'd get liquid nitrogen from a solar panel whilst underground.

Beats the living hell out of me. Though while I doubt he meant underground, if he did, then zombies wouldn't bother you anyway, just the complete and utter lack of food.