One of the consequences of believing that evil spiritual beings negotiated with God for the world to be evil (as a condition on willing temptation to exist) (which may be the best explanation for why there is so much evil in the world despite God being good, and is the one favored by MSLN) is that we wonder, what exactly did those evil beings negotiate, and to what extent do they interact with our world?
First, I want to say that if any evil beings do interact with our world, the belief that they exist, and the belief that they don't exist, are both things they would use against us. These beings want to drive us crazy, torment us, and deceive us. But that very thought can drive people crazy, torment them, and deceive them. It is good to read about deceptive truths, pathological thoughts and emotions, epiconcepts, seeing Spiritually, and gating off voices in this context. Also, any discussion of evil makes it possible to wonder if people are evil. I think it's possible that there are evil people, but it can be dangerous to identify people as being evil -- don't sell yourself out to that belief. Evil beings get their will done when people believe other people are evil when they are not. Some readers may want to rule out the possibility of there being evil beings because such a belief could be associated with a traditional religious belief in the devil. They may look on such a belief as a fear tactic, used by religious people to control people. If there are evil beings, then the fear tactic furthers the aims of evil beings, as does the avoiding of the fear tactic to the extent that we rule out the possibility of there being evil beings.
If you can, see evil, but don't fear evil. The power of evil can be reduced by seeing it without fear. If evil frightens you, you can rely on God to keep you safe.
The good news, from MSLN's point of view, is that all being follows from God, and God brings about a completely legitimate world in the end. Evil is real and substantial but is parasitic on good. Evil can never win in the end, at least, it can't destroy God and anyone who remains with God. Evil might succeed in pulling people away from God. We are born with God -- something has to overcome that starting point for us to be lost. Though evil is given a certain latitude to affect the world, one shouldn't forget that God also has latitude to affect the world. Generally people are not on the side of the evil beings, although what they are on the side of may turn out to further the purposes of the evil beings. The evil beings are limited and only one side of the war.
To answer the questions from above ("What exactly did evil beings negotiate? How much do they interact with the world?"), the bad news that is most certain, from an MSLN point of view is: There is some evil that can have an overall good effect, all things considered, but it's debatable which evils do, and it's clear enough (to me) that there is such a thing as gratuitous evil. This evil has nothing to do with human conscious choice. Natural disasters, parasites and other disease-causing organisms, the drives toward aggression and hypersexuality (or other very common biological sources of temptation), genetic-based mental illness, and so on clearly qualify for this category. These are things that we would have to pin on God himself, and in a sense, he does bring them into the world, but not by his own will. These were negotiated to be part of the world by the evil beings, as a condition for them working for God by willing our temptation.
Beyond that, MSLN doesn't have a lot of answers. So I will discuss the range of possibilities as I see it. The reader may be able to form an opinion, based on what they see, as to where in the range of possibilities the answer likely lies.
It does seem likely that if I were a group of evil beings able to have a say in how reality was going to turn out, I would include a provision for my kind to be able to do direct work.
This work might be seen in how cultures are guided. For instance, Descartes was inspired by a set of dreams to reform all knowledge according to a rationalist project (ctrl-f "dreams" to find the reference in the preceding link). Where did those dreams come from? What effect did they have? It certainly pushed history forward. While Descartes himself seems to have been a believing Christian, his intellectual project led to a lot of atheism in the years that followed. I can see God and the evil beings both wanting to get something out of rationalism. Rationalism would then be a site for spiritual warfare, a contested ground. But suppose that rationalism favors evil more than good. Then Descartes' dreams may likely have been the product of an evil spirit, offering him a tempting vision, which he trusted.
How many great minds do not work from inspiration, and where does inspiration come from, except from spirits, good, bad, or (more or less) neutral? Certainly I would expect a materialist reader to think that there are things other than "spirits" at play. But from the MSLN point of view, whatever is, follows from somebody's conscious choice. So a flash of inspiration, if it ever doesn't completely seem like you, if it "comes to you", may well have been devised by some other being. Creative or scientific people are conduits or receptacles for spirit voices, in addition to being people who can create or discover in their own right. Spiritual influence can be a good thing -- it may be a way that God influences the culture. But it can also be a bad thing, or, probably more likely, a contested thing.
Evil beings can work through people who are diagnosed with mental illnesses, producing some or all of their hallucinations and moods. Psychiatric medicines would then block the power of evil beings -- the evil beings consenting to this, I suppose, with some consolation that that established way things are done may promote the view that all mental phenomena come from the nonspiritual world.
They can also work through people with personality disorders -- the "algorithms" that drive such people might really just be evil spirits who hijack them. Such hijacked people look like they are evil, but don't intend or even remember or realize what they are doing. They make themselves look like enemies when, sometimes, they are not. Or they only have a mild or moderate enmity, which is amplified by the spirits that use them. Evil beings like getting humans to hate each other. Probably they are involved in what goes on in politics. The great scandals are probably driven in part or in whole by evil beings.
Evil beings, when they work in people's minds, work within the psychological laws which people's thoughts follow and which can be measured in the brain. Within whatever extent people can express free will outside the skein of deterministic events, there can be the free-willed action of evil beings.
Evil beings can possess people, have them in their power for years on end. They don't necessarily use people all the time, nothing that obvious. But their victims' minds are held captive, and their victims suffer attacks, and themselves are the conduits for evil into other people's lives.
Evil beings can work with people symbiotically. People can have evil intentions which are aligned with the evil beings. If you have a sinful heart at what you think is a small scale, evil beings can work with that and amplify your effect in other people. Your sinfulness is a foothold, and evil beings do not want you to repent. They want you either to ignore your sinfulness, to call it something other than sin, or to lose hope that you can really repent. And you may not always favor what the evil beings want. You may go back and forth between having good intentions and bad, and this alternation allows you to do deeper work for the evil beings, higher on the hierarchy of betrayal.
Not only is your sinfulness something that can be something that is aligned with evil beings, but also your enmity with God (if seen as separate from your sinfulness). Both, your enmity with God in intention, and your enmity with God in fact.
While we may be impressed by suffering, insanity, confusion and the hatred we have for each other, the most destructive thing evil beings can do is turn us against God. They can do this directly, by tempting us or turning us way from anti-temptations. Or culturally -- when we are deceived by them, we spread the lie that opposes the belief that God is worthy of our obedience and trust, either by consciously opposing such a belief, or by adopting it but behaving in a way unworthy of that profession of faith. Evil beings try to shut up and discredit people who follow God and who try to proclaim God's glory and the need for God.
How widespread is this evil? Certainly there are obvious cases, but if the goal of the evil beings is partially to deceive, aren't quiet deceptions better than loud ones? So it may be that in subtle ways, we are being lied to, and don't realize it.
Evil beings can work on small scales or in coordinated actions on large scales. Leaders are especially targeted, because of their disproportionate effect on other people. Evil beings prefer to hide, at least in Western cultures.
It could be that all of the evil beings are unified. It is also possible that they have factions or political parties, or even schismatic movements. Evil beings may oppose each other, while still intending to oppose God. I'm not sure we would see evidence of this, but we might.
God can certainly interact with all beings just for being the mind through which all beings experience. But how can the evil beings get around to so many of us? One possibility is that just as human persons are created and brought into the world, so are evil beings. Maybe God creates them, under contract from the evil beings, or maybe they create their own. God is the original person, the original source of all personality, but evil beings may still be able to create on their own, out of the personality that originally came from him.
So there may be enough evil beings for all of us to be affected by their specific work.
Again, these are speculations, which can fit into the non-biblical parts of MSLN, but you can see how much you think your experiences bear them out.
How could this connect to the Bible? In the Bible, sometimes "the devil" or "Satan" is referred to. The devil seems to be singular, as though there is one demigod that is parasitic on God. But there is also mention of multiple smaller demons. So there are plural evil beings in the Bible, just as in the non-biblical parts of MSLN discussed above.