Tectonic Fragdrill

The only logical way that this thing can cause earthquakes is to imagine it as a miniature cyclonic torpedo.

Less of a vehicle and more of a earthquake making machine, the Tectonic Fragdrill can make a pinpoint assault on the most volatile parts of the planet’s crust, resulting in a localized earthquake. How a machine this small can generate an earthquake (even a small one) is up in the air. The answer might be mundane, it might be space magic, and on the other hand it might be bullshit.

Hell, even as a industrial mining machine, the design makes no sense. Like, why the hell are there three drills? Not only that, but why the hell does one of them look like a screwdriver mounted on a flimsy arm-piece? It doesn't appear to be a versatile and durable machine. It's highly unlikely something like that could even drill past granite, let alone a planet's crust, given its design.

Overview

Nevertheless, the Tectonic Fragdrills are often mounted on a specially designed base that helps positions the machine before punching through the ground via a rail harness. You can think of it as an elevator of doom. It's unknown how the Imperium could get these machines back to the surface, although the most likely answer is that they are meant to be disposable, acting like a giant underground missile. Modern artificial seismicity is often caused by dumping a very large body of water (like a dam), inducing artificial sinkholes through sufficient underground mining and coring, and most infamously, setting off an underground nuclear blast. So the Tectonic Fragdrill being an underground nuclear ICBM could be the most reasonable answer of it being able to create an earthquake.

Given the 8th edition rules, however, it is more like a Genestealer Termite than an underground nuke. This is due to how it is used to create underground caverns for Genestealer Cultists to launch a surprise attack from below. Just don't ask us how they manage to tow the damned drill back. It's possible they didn't, since the drill has now been officially squatted in 9th.

Because of how much Genestealer Cults love to work at mining and industrial jobs (FOR. OBVIOUS. REASONS.), they have learned to harness these machines to cause maximum disruption to their foes on the battlefield, causing entire building foundations to collapse or creating a large sinkhole.

Tabletop

The Fragdrill is played more as a useful offensive terrain than an actual vehicle or machine. It has a couple of cool abilities that allow for some sneaky re-deployments, and it can mess with your opponent's ability to charge. This ability is called Underground Ingress. Once per turn during the Movement Phase, one infantry or biker unit with a Cult Ambush ability can move off the battlefield if all of its models are on ground level and can move within 1" of this model (a unit cannot do so in the same phase it arrive as reinforcements). Once this is done, remove the selected unit from the battlefield and at the end of your Movement Phase, you can set up that unit anywhere on the battlefield that is more than 9" from the enemy models. If the battle ends before this unit is set back up, it is destroyed. For all intents and purposes, it is an underground deepstrike.

The first secondary ability is Seismic Tremors, which subtracts 2 from charge rolls made for units whilst they are within 12" of the Fragdrill. Flyers are obviously not effected by it and the effects of multiple Siesmic Tremors are not cumulative. The second secondary ability is called Seismic Quake which is the offensive ability. It also has one of the weirdest ways to attack, for you need to draw a straight imaginary line from any point of one battlefield edge to any point of another battlefield edge in such a way that it crosses this model. You then roll a D6 for every unit this line crosses that is on ground level (Flyers exempted as usual): on a 4+ that unit suffers D3 mortal wounds and its Move characteristic is halved until the end of its next Movement Phase.

Basically, this piece of machinery is there to fuck speedy assault-oriented armies over. Say goodbye to fucking successful charges Khornate Warbands, Ork WAAAAAGHS!, Bishonen Vampires, Space Furries, and BDSM Space Elves, because now half of your entire forces are stuck foot-slogging across the entire battlefield. We can foresee this machine being Grade A fucking annoying to deal with if you're a melee army. Not so much if you're an army that prioritize flyers or just stands there launching an ungodly amount of explosives at that eyesore of a drill.