I would suggest trying mad synergy by combining Galamiel and Viscerality together. Both run on inner drives and passions, there's probably some combo of stuff that works out.
You have to consider two things when coming up with ideas. The first is idea of variability that is inherent to Contamination. The results of Contamination are largely random, and understanding how they are random is important when combining it with things. Using Contamination to turn iron into steel is not random because we can just do it, and using Contamination to turn air into something fucked up is somewhat random, however we have variability going our way as Contamination usually expresses itself by making things hostile. The second thing is that each action we take should ultimately have a measurable outcome that helps our overall goal of defeating the knight.
Just randomly using Contamination of Viscerality doesn't really clear either of these goals. Variability doesn't lean towards "Viscerality is improved enough to be combat relevant" so we are trying to randomly do something that is not likely to happen, and even if did happen we don't really accomplish any goal that helps us actually beat the knight. Understanding how Contamination variability works and how you should look forward to solutions and not just random ideas, is the key to figuring out useful strategies.
I think the corrupting the masks has merit, the guy is asking for two after all. We give him what he wants, and contaminate unravelling them into facelessness explosion. Lets see how people deal with an esoteric attack like that.
We also need to consider the narrative implications of fearlessness, if we use that to negate the aura. Is that a protag we want to play moving forward? I can see pros and cons of Dorian losing his sense of fear.
edit: The elf girl is fated to die - all of the prisoners are fated to die gruesomely and doom some world. A kindness would be to end their lives here and now. Instead of her unleashing the plague later - we could contaminate prim her to unleash now in a different fashion - that could conceivably harm the deathknight. He is giving them to us after, they're ours to do as we please. And afterwards we can trigger the masks as well.
Funnily enough, I've also consider Contaminating their plague. Ultimately, however, knight seems to be capable of manipulating plagues himself, so I don't think that this will work.
There are three things we need to cover with our tactics: beginning of fight, fight and finale.
Beginning of fight basically deals with fear aura. There are two outcomes here - either we can deal with aura, or we need to resist fear ourselves. Former is vastly superior option as we drastically increase amount of variables that favor us, as we can include Musurov and plaguebearers to the mix. To counter aura, we need to either use Contamination on it directly to make it less harmful to us, or to somehow mess up medium used to propagate its effect in order to render its range useless. To counter its effect on us, we need to either Contaminate our fear, or increase our willpower in some way. Theoretically we could also use Viscerality to remove our ability to feel fear, but I'm afraid such feat is likely beyond our current selves.
Fight covers how we actually engage with the knight. There are three possible situations here, following from the first point - we have either completely nullified the aura, in which case we get all the people to fight and we can use Contamination against the knight, we have nullified aura but we require constant use of Contamination, in which case we get others fighting but we can't use contamination, or we have rendered ourselves immune to the aura, in which case we get to use Contamination, but we are in 1v1 and probably fucked. There are also scenarios in which we could apply our solution to fear to Musurov, which would help us immensely, but that's pretty ???.
For the fight, we have following: Masks(we could lend them to other people), CL boosts combat(give it to dragon? or use it ourselves), Icarelian gives light manipulation(give it to Musurov), Contamination(we can Contaminate air into some kind of toxin or liquid Musurov could manipulate, or shackles into something for their magnetism, we can contaminate masks we have etc), our combat stats(likely low), Musurov(long range lightning attacks and similar) as well as prisoners(useful as chaff). Coming up with new ways to fight is crucial
Finale is how we actually put the knight down. Turning Artificer into combat Facelessness mask then consuming bunch of faceless mask we have to power it sounds like a great idea, using Contamination to generate gas Musurov can ignite within knight's lungs is likely too cheesy to work, giving CL to lizard guy and then using Contamination to buff him even more might do it, although then we will have other problems, or if everything else fails corrupting this part of Street to yeet him into some fucked up hellhole.
Hellhole was 666th word of this post, funnily enough.
