I suspect this card provides more utility in some campaigns than we might give credit for, though this depends on my (possibly incorrect) rules interpretation.

Haunted is the clear location effect that would trigger during the test. As I understand it, Haunted does trigger during the skill test. Specifically Step 6 (Determine success/failure of skill test).

Relevant text from the advanced skill test rules reference:

Reaction or Forced abilities with a triggering condition dependent upon the skill test being successful or unsuccessful (such as "After you successfully investigate," or "After you fail a skill test by 2 or more") do not trigger at this time [Step 7]. These abilities are triggered during Step 6, "Determine success/failure of skill test."

So, if playing The Circle Undone as a mystic this might actually warrant consideration for your deck. Bonus that it's both a keyword and location effect.

Looking through a small sample of Dunwich and The Circle Undone locations, it's clear there are numerous locations with effects occurring during step 6, typically contingent on failing the test.

There's another hidden benefit that might go overlooked on many locations. Locations are largely the fulcrum for clues and clue interaction. This is where you're investigating the vast majority of the time, and so are designed to commonly trigger on picking up one or more clues. Since picking up the clues occurs during Step 7 (Apply skill test results), and the skill test does not end until Step 8, you should be able to safely ignore those negative effects when testing with Mesmeric Influence.

A ton of locations care about whether you pick up a clue.

I am not an expert, but if you combine Cloak of Resonance (new core) with Agnes Baker (old core), you get a pretty powerful combo:

1) Agnes takes an horror --> ennemy takes a damage

2) Move horror onto cloak of resonance using lucky charm --> ennemy takes another damage

On the next turn, you can even place this horror back to Agnes etc. which basically gives you a free damage each turn.

If you play with an investigator which has low sanity, you can even heal your ally... It seems very handy to me.

This card is very good with Agatha signature Ocula Obscura. You basically get 1 free charge spell and 1 guarantee 3 damages once per tern(Might be more, if you can find a way to ready Ocula Obscura). However you need to fish for 0 token first, which is not difficult if you run Breath of the Sleeper or Eyes of the Dreamer.

Ravenous Myconid came out with it's bonded event card Uncanny Growth which comes with a bolded Investigate action on it to power up the myconid. You are able to return Uncanny Growth to back to your hand every turn using Ravenous Myconid's fast ability (Like how Dream Diary works). This effectively gives you a guaranteed free investigate action each turn when you use Uncanny Growth with Farsight. On top of that, you power up the Myconid more each time that you do it. It's a near perfect synergy, close to broken though.

I have only played this card in ONE deck. and that deck was shotgun Harrigan where it performed pretty well actually.

I was all in on shotgun, which late in the campaign included a custom modification, custom ammunition and an enchant weapon.

So I was frequently dolling out 5-8 damage on basically any attack, making relentless actually kinda good as every enemy slain was being massively overkilled, I once discarded relentless for about 20-something resources.....

In most other decks this card is bad. Most decks are not built around over-killing enemies becuase well.... Overkilling usually means you spent more effort than it was worth to kill something, in which case getting compensated 1 resource per damage is not a great rate.

Would love it if they made an XP version of this card though.