One of the great mysteries left to referees to decide on in Luther Arkwright campaigns is what the larger master plan of the Disruptors is. This is partly because the source material doesn't specify it, and partly so you can make it whatever you want it to be in your own campaigns. I did some thinking about it based on playing a bunch of Luther Arkwright and planning a bunch of one-shots, and wanted to lay out what I decided what I think makes sense in the sort of games I'm interested in running. The idea of all of the following is to give one ideas for Luther Arkwright plots that Valhalla agents can stop, in case that isn't apparent.
In broad strokes, I see the Disruptors are trying to collapse all of the infinite possibilities of the multiverse into one parallel, one where they are utterly triumphant and all-powerful. Once they have discovered this parallel, they will destroy all other parallels and become gods in the remaining universe.
To do this, they undertake several kinds of large-scale missions and campaigns.
1) Destroy parallels with a low-probability of becoming the "right" one, ideally after first harvesting all useful resources from them. This releases the psionic energy bound up in the parallel and distributes it back across the multiverse. These sorts of parallels are also probably the ones where they're doing their most strenuous and large-scale experimentation, like running genocidal eugenics programs on entire worlds to see if they can improve the rate at which psychics are born, or
2) Testing different historical developments to see which increases the probability of a parallel becoming their ideal-universe. This means both encouraging convergent developments that they know increase their possibility of success, while experimenting with new developments and new parallels to ensure they are not stuck in a local pseudo-stable maxima (that is, a course of development that seems to be progressing in the right direction but which ultimately turns out to plateau before success is reached).
3) Experimenting with the occasional high-risk, high-reward, parallel in case doing so pays off (parallels where aliens powerful to challenge them exist, parallels with lots of psionically-aware people, technologically advanced parallels sufficient to compete with them scientifically and militarily, etc.).
4) Infiltrating parallels where their enemies, potential competitors, or serious resistance to them is available, undermining the capacity of these forces to fight them by destabilising these parallels politically or otherwise, and eventually either destroying or isolating them from the multiverse.
To break these down further:
Destroying low-probability parallels
These operations first require an assessment of the situation culminating in an analysis of its probability of Disruptor success. After that, the Disruptors will attempt to strip the parallel of any useful resources, and neutralise or avoid any major threats to doing so. After that, the Disruptors must destroy the parallel, which means somehow causing the psionic energy that maintains its existence to disperse.
Dispersing the psionic energy can be done in a variety of ways. The first is to find some highly psionically active and powerful entity or object, perhaps a multiversal constant or a powerful spirit, and cause a psionic energy feedback loop that "explodes" the parallel. This might involve importing additional psionic energy from another parallel, or concentrating much of the psionic energy of a given parallel into a small area. The second option is to construct some device, or bring in some psionic entity, that will drain the parallel's psionic energy back into the multiverse. The device might operate according to impossible physical laws that the host parallel can't accommodate, or it might link two parallels and transfer the energy from one to the other. A third would be simply to kill every psionically active entity (every living thing) in a given parallel, and then simply wait for it to dissolve.
Utilising these parallels for the Disruptors probably falls into a couple of main methods. The first is grabbing or using any unique features of the parallel. Are there connections to more valuable parallels that can only be reached via this one? Technology from long-dead aliens? The second is running damaging and awful experiments. These are the sorts of parallels that are candidates for the Disruptors to use as vast eugenics farms to experiment with the birth rate of psionically active people, to test their most horrific and devastating weapons and tools on, and to examine the most dangerous unknown artifacts that they've recovered from the rest of the multiverse. The third is just straightforward economic exploitation - the enslavement of entire worlds to turn out the weapons of war for dominating the rest.
Valhalla is no doubt very interested in preserving these parallels, since they offer the least gain to the Disruptors' plans. Without the active interference of the Disruptors in exploiting and destroying them, these parallels get along just fine.
Converging and collapsing history
Boosting any given parallels chances of becoming the ideal-universe for the Disruptors probably take several forms. The first step is establishing whether the parallel is a good candidate for the ideal-universe. We know the Disruptors like powerful, hierarchical governments, preferably as few as possible, that they can take control of secretly. They also seem to prefer parallels where technological and scientific development can be made beholden to Disruptor influence. Worlds teeming with people, who produce a lot of psionic energy the Disruptors can utilise, are also ideal. The second is changing the world to better suit their needs. This means introducing various multiversal constants if they don't already exist, or aligning them with the ideal-form of each constant if they're slight deviations. It also means taking over the governments of the world. Chances are, the Disruptors also look for worlds with lots of psionic connections to other parallels that they can send psionic influence through. I figure there are probably "anchor" parallels that serve as the local node through which a series of parallels with minor deviations are connected (e.g. a bunch of worlds that are almost identical except for small quantum variations).
Once they have them under their control, the Disruptors are probably seeking to prevent them from deviating from developing into the ideal-universe. My basic assumption is that the Disruptors can't reliably see the future (except insofar as psionics allowed very limited precognition). So they don't know which one will pan out as the ideal, and have to constantly adjust and readjust their development in line with what they predict, but can't know, is the ideal course. Some will fail, of course - Valhalla or others will free them and drive the Disruptors out, asteroids will destroy others, and others will turn out to be pseudo-stable local maxima that will plateau rather than continue to develop into the ideal-universe.
I expect that ODIN, Valhalla's supercomputer, is pretty savvy to what these parallels look like, and can even guess how far along the Disruptors' plan is based on an in-depth study of its history. While these are the toughest nuts to crack, Valhalla gets the most gain when it manages to flip one of these from a high-probability parallel to a low-probability one, either by eliminating the Disruptors' control, or undermining their development and forcing them into pseudo-stable local maxima.
Experimenting with high-risk, high-reward parallels
These are parallels that are so unique or unusual that the chances of them becoming the ideal-universe are extremely low, but that can't be written off for all that. Worlds where the entire population is psionic, or powerful aliens friendly to the Disruptor cause are willing to trade unusual technology, or where technology is 10,000 years more advanced than our own world, or where some species other than humanity has dominated the planet. Depending on the multiversal savvy of the entities running these parallels and the resources they command, the Disruptors are probably more or less aggressive. Attacking an enemy who can chase you through the parallels with glowing clouds of mind force is stupid - trade or wary observation are more likely. On the other hand, even a galactic federation of energy beings can be conquered if you can simply retreat to another parallel and regroup safely whenever they start to make gains. Some worlds are also weird enough that the Disruptors probably have a small monitoring presence to continuously evaluate and nudge their development towards the ideal-universe, but little more.
This class also includes parallels like the one that Firefrost was found on, where the main interest is in some one thing that's super-powerful and is way more interesting and important than the rest of the parallel would be in its own right. In these cases, the Disruptors would only bother to get enough control to find and control that one thing, extract it to their home base, and then send a clean-up team to eliminate the parallel like any other low-probability parallel.
Some of these worlds will also be ones where a small group of Disruptors with a heterodox vision of the ideal-universe might be operating. You might have a small clique of knights and bishops who've taken control of a parallel (or at least a large part of it) and are using it to prove the superiority of their ideas versus the mainline Disruptor vision of development. If this parallel does well (by Disruptor standards) they'll be vindicated and rewarded, while if it deviates into a low-probability parallel or plateaus, they're liable to be punished for their heresy.
These are also the sorts of worlds that Valhalla is likely to send agents to for other reasons - trading with the aliens or super-intelligent chimpanzee empire, or whatever - who then stumble across Disruptor schemes. Or Valhalla agents might go on a variety of missions to deny the Disruptors whatever key resource they're drawing from this world.
Undermining the opposition
Parallels where the opposition to the Disruptors is organised and effective are no doubt their worst nightmare, with the absolute nadir for them being a parallel where the original aliens opposing them way back when succeeded without perishing. You probably see an escalation here, as the Disruptors go from identifying and analysing the opposition to adopting a plan to destroy them, and if that fails, seeking to destroy or isolate the parallel itself. 00-00-00, Valhalla's home parallel, is the most well-known of these in the Luther Arkwright universe, but we can assume there are others (heck, there's probably at least one more Valhalla out there).
Interestingly, it seems like a lot of parallels with alien contact and/or powerful psionics probably fall into this category. Disruptor control is probably highly contested, though they may have footprints in governments or other power centres that allow them to strike out at the opposition. In some of these worlds, the Disruptors will be trying to "flip" their enemies into allies, or at least neutralising them, perhaps by offering them resources they otherwise lack. In others, they may be trying to destabilise the mundane governments and institutions of the world to gin up chaos and destroy the support system that their opposition relies on to be effective.
Valhalla agents are no doubt assigned to get out there and form alliances with these groups, as well as to study their technologies and methods that make them so dangerous to the Disruptors. Once they are identified and alliances made, agents will no doubt have to occasionally go and help their allies fight off Disruptor plots to undermine or destroy their parallels.
Mixing and matching ideas from the above categories can help you put together a consistent and interesting set of Disruptor operations that either span several parallels or deeply engage with a single one.