So, in one of our games, we're fighting a bunch of people made from Bismuth. They're reasonably homogeneous in structure.
It was suggested that we build swarms of drones to combat the problem. I discounted the idea, not for in setting reasons, but because it was another way for our party to avoid combat. The game itself was already turning into spreadsheets, the game, so it was obviously quite dull when it came to only a couple of party members doing anything.
However, we went ahead with the idea anyway. My own lack of sleep and medication resulted in some ideas taking a dark turn. What if we could make drones that didn't simply explode, but turned our enemies into more of themselves? Using some relatively easy to follow rules, and perhaps a neural net, you could easily have a very John Carpenter's the thing scenario.
The Bismuth aliens (henceforth, bisnauts) did in fact have a "brain" part of themselves. It uses magnetic impulses to cascade through their brain structure, altering it and affecting parts around it similar (but not entirely the same) as neurons do in human brains. This brain, in turn, has larger scale magnetic impulses that allow the bismuth "muscles" to move. This structure makes the aliens very hardy and quite smart, but not very creative (I guess that's how I'd put it).
This drone would basically latch on to a part of a bisnaut, say an arm or a leg, and overpower those magnetic impulses to control the limb. Were enough force put into it, it could simply take the offending limb. Obviously, the drone would have to have a much higher energy output than the bisnauts themselves, making it relatively low endurance. However, once it had taken the limb and all the new bismuth (as well as any magnetic energy stored in the limb), it could then change and warp the limb to suit its own purposes.
The first thing it would do is create a simple neural net inside its new limb. This would allow the limb to then act like the drone, even when on its own (albeit very limited). Thus, the drone, with its ramshackle collection of limbs and other bisnaut parts, would grow. It could also split off into smaller parts to facilitate infiltration and area denial.
Inside the neural net, which would form a brain, sort of, you'd have a lot of data on how to build a number of basic things. For instance, the drone would need to know how to "build" an eye for itself.
It would also have its "instincts".
Self-preservation: The drone would take cover, use hide and ambush tactics, and all sorts of things to make sure it survives. This would be weighted depending on its current magnetic energy reserves and how much usable bismuth it has acquired.
Hunt Bismuth: The drone would try to acquire as much bismuth as possible. Again, this would be weighted depending on the other two and how much bismuth it already had. All things equal, though, and this instinct would be top priority (its the drone's "goal" to get large).
Hunt Magnets: Bisnauts are basically charged up by oscillating magnetic fields. While they can have "too much", their ability to store energy is quite high. The drone itself would expend energy at quite a high rate, especially when hunting or growing (lying in wait would be an option). Given the drone's quarry, it shouldn't have too much problem finding energy sources.
I'm not entirely sure what to call this thing. I'm sure the DoD's naming department could come up with something catchy for it.