Voodoo Remoras
Naturally, these devices are neither the product of any sort of syncretic spirit-based religion, nor made up of actual scavenger fish. A Voodoo Remora isn’t even organic: it’s all raw galvanic fluid and platinum and gold aetheric current wiring and the rest of the old-style Mad Science aesthetic. Just, you know, updated with 21st century manufacturing. Fortunately, most Mad Scientists can’t make the conceptual leap that lets them realize that, just because their science is steeped in pre-Einsteinian physics, their engineering and machining doesn’t have to be late Victorian-era as well.
Anyway, a Voodoo Remora works as follows: take a shark. Attach a Voodoo Remora to it. Watch, dispassionately, as the shark dies of a cerebral hemorrhage via the implantation process. Wait until the Voodoo Remora finishes patching itself into the shark’s nervous system. Turn on the dedicated viewer / controller. Congratulations! You now have your very own zombie shark.
When not under direct control it will vaguely do the things that normal sharks do, but you can take it over at any time and make it swim and bite and, well, that’s more or less what your average Mad Scientist wants to make a zombie shark do. Since the shark is dead, eventually it will fall apart. Unless other sharks eat it first. Or it explodes when decay gas buildup in the tissues exceeds the local water pressure.
Obviously, Mad Scientists mostly use Voodoo Remoras to get themselves an undead shark army. Which usually turns into an undead shark platoon, because Remoras are hard to make, and expensive as all get-out. But then, it’s really not about world domination, is it? It’s about having zombie sharks guarding your undersea lair. Voodoo Remoras are very much mostly for the look of the thing.
Well. For a given value of ‘look.’
Does it scale? Could you put a VR on a sperm whale and get a zombie Moby Dick or is that to large? How about a giant squid for a zombie Kraken or is that to many limbs?
I’d think each new distinct beast would require a lot of expensive adjustments. Consider the device driver issues between a shark, a cetacean, and a cephalopod. And that’s assuming you could even try to adapt the code without publishing your source under the Gnu Public License.
What? Of course mad scientists would follow the GPL’s license terms. What good is being a mad programmer if you don’t open source your work? How can those fools at the Debian project rue the day they deprecated Iceweasel if you don’t contribute your code?
Hmm. Even though this is technology, rather than magic based, imagine the GPL in a magic world, applied to spells. Where the obligations are enforced via a geas or other binding. You could make it work in the Laundry Files fairly well.