Mysteries Abound

My take on this set: Mysteries Abound is a set that interacts with the concealed mechanic without having any concealed cards itself. It gains a lot of its value not just from other encounter sets, but also from the scenario it is used in, for example in Buenos Aires the Envoy helps La Chica Roja hide in the shadows while In Plain Sight will make her attack when she’s eventually uncovered anyways.
This isn’t a particularly impactful encounter set on average, but the Envoy sure has his moments.

What it does: Coterie Envoy is quite untypical for this campaign, one of the few Coterie members that doesn’t start in the shadows. He has low fight and evade, however between Aloof and 3 health he still requires some effort to defeat. While ready, he protects mini-cards at his location from being revealed and should there be none at his location, he patrols towards the nearest one during the enemy phase.
As an upside, defeating the Envoy allows the player to peek at the face-down side of a mini-card in play.

My take: What a weird enemy. Coterie Envoy doesn’t pose a threat by itself, but by stopping players from revealing concealed enemies at his location he does slow down the team considerably anyways. Dealing with Envoy will often take away a full turn, spent on engaging and attacking twice. This is made up partially by that ability to peek at a card in play which can be a huge help in both scenarios he is in.

Threat level: Mid. Not dangerous as such, but he’s a time-waster that makes the cards that are in the shadows more effective.

Dealing with it: Whenever i see an aloof enemy with 3 health, i just want to Spectral Razor it. Aside from having a card tailored to the job like Razor (or at least Get Over Here) available, the amount of effort required to defeat Envoy means that it can be attractive to just let him stick and reveal the other mini-cards in play instead. After all, the Envoy might only be protecting a decoy and without specific knowledge otherwise it might just be easier to look elsewhere.
Obviously that isn’t always possible and you might need to go through the Envoy to progress the scenario. In that case, it’s at least not difficult to do so, it just requires a turns worth of actions.

What it does: In Plain Sight attaches to an enemy in the shadows and will make it attack when revealed. The enemy will also gain +2 fight for the turn it got triggered.
If there is no valid target for the card to attach to, it surges.

My take: In most cases, this isn’t something that you get to interact with very much. It’s simply a damage/horror treachery that is testless and variable, but also delayed. This can inform who in the team should do the exposing, but one way or another this extra attack is going to fire usually.
If it’s just a damage or horror (like most concealed non-unique enemies have), then that is perfectly fine. If it attaches to one of the unique enemies (Tzu San seems to just loooove this card) the fight bonus can also be significant in addition to the extra attack.

Threat level: Low. Just a point of damage/horror in most cases. Even when it’s more the delayed effect allows players to time it and to have it affect whoever can take it the best.

Dealing with it: It’s a damage/horror treachery and not one that deals a lot of one type at the same time. So this should be easy enough to soak or just take on the chin. Obviously it becomes a bigger issue as part of a critical mass of damage/horror dealt by the encounter deck. Buenos Aires can get a bit dicey with La Chica Roja attacking from the shadows and having as much soak as possible to survive the Shade Reaper is also important. But there’s probably more important factors than In Plain Sight to care about.