Not a fan, has too many things going against it.

1. You need to defeat a Monster enemy only. You won't always find one of those.
2. You need to defeat the enemy, not another investigator.
3. You need to have card in hand, and 1 resource at the time (guardian's tend to run low on resources)
4. The enemy must have horror value, there are some that don't (but fortunately, most Monsters do, maybe 75%)
5. You only heal 1-2 horror on average. Usually only bosses give 3 and if you're killing a boss you probably don't need the horror heal anymore.

If you can/own the cards, you're probably better off playing Book of Psalms, Hallowed Mirror, or Medical Student
Out of faction, you can try Logical Reasoning, or Fearless

Interesting that this card was released 4 years before the investigator on the image, yet still gave indications on her Stats: all but and what she likes: being engaged with a lot of enemies.

I mean thematically, this card is amazing, she looks cool af on the artwork, so does the Mechanic's Wrench, and the card does what turned into: high number of Icons skills (look at the Synergy card for : Strength in Numbers, one of the least broken yet one of the ones I've used the most so far).

Still, compared to the 3-icons Skills, this one is by far the weakest: Inspiring Presence that I add to increasingly more Decks lately and the staples "Watch this!", Eureka! and Resourceful. It doesn't bring anything to the success and takes 2 enemies on you to overshoot Unexpected Courage, which doesn't come that often, and if it does, high numbers are not necessarily what you're craving for.

Now, will I add this card to Daniela Reyes' Deck? Probably not because there's much better to do with her 5 lvl 0 cards and Strength in Numbers is much more likely to give a better boost for 1 pip, but I still love the Artwork and I almost wish it was the one selected for the Mechanic's Wrench.

A hard to evaluate weakness that leans more into the investigator's mechanics than her flavor. Looking at the two elements, the effect and the discard condition, we get:

The effect: You either break one of Lily's Disciplines, or you take a damage and a horror. Neither of these are terrible; it's usually more annoying than difficult to flip a Broken card (with the notable exception of Quiescence of Thought, and even there you might draw the ). Losing the bonus or a use of a Discipline's power might cost you tempo or a test, but it's not too likely to cost you a scenario. Similarly, with the card pool, Lily has access to soak and healing to handle a couple of hits. The problem is that. as you build up XP, you get more of these. One is pretty trivial, but drawing a couple in close succession might put Lily in jeopardy (although less so than Thrice-Damned Curiosity or Shell Shock. Additionally, they cause increasing dead draws, especially in scenarios that like to put extra weaknesses in the deck. In The Path to Carcosa, if Lily is lead investigator, she could easily end the campaign with a 37 card deck, 7 of which are weaknesses, and Lily doesn't have a lot of card draw in her classes, and usually has a moderately large rig to get out before she really shines.

The discard condition: Make your decision and then discard it; unfortunately, you probably have 1-2 more copies waiting for you.

All in all, this is a below average signature weakness, more likely to annoy you and slow you down than really capsize a campaign.

This is not the worst treachery in the game; it's often very mild, especially compared to things like Psychopomp's Song and Death Approaches, since you can often get it on an act or agenda ready to advance, but the artwork always makes me smile; it's funny and chilling.

If this card lasted until the end of that investigators turn, maybe it would see play in multiplayer if your friend is prepared to blast things with his shotgun (which also doesn't see much play), but sadly it is unplayable in this current form.