Nameless Horrors

My take on this set: This set is nasty. The Tekeli-li weaknesses have a wide range of detrimental effects and Nameless Horrors is one of the sets that is best at making those weaknesses really hurt. This leads to basically losing draws and getting bombarded with these effects that range from a point of damage to discarding assets or losing actions. Two of the three cards in Nameless Horrors make Tekeli cards double up on their effects, turning even the weaker Tekeli-li into respectable weaknesses.
Due to impact and how often it is used, Nameless Horrors is one of the signature sets of Edge of the Earth to me.

What it does: The investigator shuffles the top Tekeli-li card into their deck, then puts Blasphemous Visions into their threat area. While affected by the treachery, the player has to resolve all Tekeli-li card they draw twice.
To discard Blasphemous Visions, any investigator at its location can spend and action and pass a willpower test.

My take: Since it does come with a complimentary Tekeli weakness itself, drawing it will never be a full freebie. Going from that floor, the impact of this card is going to vary wildly depending on how many Tekeli-li cards you already picked up. Doubling the effect of those weaknesses can be really nasty and you generally will want to spend the action to clear Blasphemous Visions from the board if you can reliably pass the Willpower test.

Threat level: Medium. There’s a good deal of variance with this one, not only depending on how many Tekeli weaknesses you have, but also which ones.

Dealing with it: So what Tekeli weaknesses do you already have in your deck? If Visions just ends up dealing an extra damage/horror or two then it wasn’t a huge deal. If it makes you discard extra assets from play or eats up additional actions, you will wish you got rid of the card beforehand. This is an impactful card and deciding on a best course of action isn’t always easy especially since there’s going to be at least one unknown Tekeli card in your deck after drawing Visions. Glimpse the Unthinkable can also be fairly awful. So can the Shoggoths in City of Elder Things, for that matter.

What it does: The player draws the top Tekeli-li card and resolves it immediately. Then, that weakness is shuffled into a player’s deck instead of moving it back to the Tekeli-li deck. That can be any player’s deck, not necessarily the one of the player that drew the treachery.
If no weakness is drawn by this treachery, it gains surge.

My take: Double dipping on a Tekeli weakness can be rather impactful and cause you to lose actions, assets or cards in hand. And even the testless horror and damage will absolutely add up over time. Since it adds a weakness to your deck it will also cost you a draw down the line. Add in the interaction with Blasphemous Visions and you end up with a card that will usually cause an above average amount of disruption to the player who drew it. There’s a little silver lining here as it allows pushing the Tekeli into any player’s deck. This is one of the rare occurrences where you gain such a weakness while knowing which one it is exactly, so you can give it to the player who is best able to handle it.

Threat level: Medium to High. This card does a lot at the same time. While it’s not all immediately pressing right when you draw it, the effects add up to something that is way above what you’d usually expect from your typical treachery.

Dealing with it: There’s not a whole lot to do about this card. There aren’t any tests on it and Peril even makes it difficult to cancel. I’d say the best way to prepare for this card is by not letting Blasphemous Visions linger in your threat area for longer than necessary. Aside from that, you’ll just have to roll with the punches here. Danforth can help with that.
The most important decision to make here is who gets to add the card to their deck. Due to Peril, the player has to make that decision on their own and they will have to gauge who suffers from it the least.

What it does: The player has to choose between either losing 2 actions immediately or shuffling the two top Tekeli-li cards into their deck. Nightmarish Vapors has Peril, so they have to make this decision on their own.

My take: Two actions is enough of a penalty that you’ll often end up seeing no other way than taking the second option. That being said, you should take the first one whenever you reasonably can do so. Drawing Tekeli-li later on will make you virtually skip your draw for that turn (~ roughly equal to an action, a bit less) and also do whatever that Tekeli-li does on top. Which might just be losing more actions or even assets.

Threat level: Mid to High. Again, losing two actions is above average for treacheries and Vapors will often end up doing more than just that.

Dealing with it: The card says “choose one” but often there’s not much of an actual choice here depending on your circumstances. Except for Fatal Mirage, the scenarios this set is used in do feature a notable amount of Hunter enemies and skipping two thirds of your turn might just not be feasible. Forbidden Peaks doesn’t look too kindly on anyone wasting their actions this way either. Especially during Peaks i would be leaning hard towards just shuffling in the weaknesses, pushing on and hopefully deal with the weaknesses in a later scenario. That being said, if you find yourself in a situation where losing two actions wouldn’t put you in immediate danger, you should probably go for the first option.