This might be easy to misread, so just a clarification.

Taking -2 Sanity is not the same as being dealt horror, I.E this is not horror you suffer or a permanent reduction in horror health. Therefore the net benefit of St. Hubert's Key is:

+

+

+2 sanity.

In other words, this card gives you the exact same benefit as a Holy Rosary, and then throws in the extra +1. The difference is however that St. Hubert's Key self-destructs and automatically heals you when you hit your reduced Sanity threshold, thus while St. Hubert's Key gives you a bunch of extra power and safety you must still be careful or you'll loose it faster then you'dd like.

St. Hubert's Key does not invalidate Holy Rosary, the latter is still a much tougher asset than the former and in the mystic's already expensive lineup of key assets finding the extra cash to pay for an often unused boost is hard. Often the St. Hubert's Key will find itself sought after by non- characters like Daisy Walker, "Ashcan" Pete or Rex Murphy who will better appreciate the extra since they spend a lot of their time using that skill to begin with. Note that the reduced Sanity stat has an interesting interaction with Desperate cards (Like Reckless Assault).

Currently the lineup of character's will prioritize tests over tests, and often paying the extra cash will just be a waste, since you will spend a lot of your time utilizing a Rite of Seeking or the like. Note that your experience with this card will vary with difficulty, an of 4 for example (like Jim Culver or Father Mateo with the St. Hubert's Key) will get you much further against difficulty 2 locations in standard than it does in hard and it'll be much easier to bridge the gap for higher difficulty locations with other cards. An of 4 will succeed on a difficulty 2 investigate in The Gathering 80% of the time on standard but just 60% of the time in hard, that's the difference between finishing a 2 clue location (Study) in one round or two.

Final evaluation: St. Hubert's Key is powerful, absolutely, but not always useful. Perhap's it is St. Hubert's Key's downfall that Holy Rosary exists.

EDIT: Bonus note, give special consideration to St. Hubert's Key in solo, especially Solo on standard.

I ran this card with... Daisy Walker ! And it's pretty good. The -2 sanity penalty is really not an issue, as Daisy have a sizeable pool of it. Then, you don't die already if defeated by horror. So that's ok, just be a bit more cautious. Or not. Because you get a +1 and +1 , two important stats for Daisy. It fills your accessory slot, which is not contested in most Daisy's deck, as I generally find this better than Holy Rosary. It's 2 resources more, but the static boost is better. On the 5 top Daisy decks on this site, 3 have the Holy Rosary and the other two no accessory.

Since this card has been spoiled i managed to proxy it and play a few times in Jim Culver deck and it turned out to be pretty good. In builds i usually use Jim investigates using and fights using . So this card boosts two of those critical stats add Alyssa Graham and you don't even have to use seeker cards for investigating, freeing up 5 flexible slots. Lowered sanity doesn't really hurt. The biggest downside is cost of 4 resources but it's really worth paying that much.

If I’m reading this right (please feel free to tell me otherwise) ‘when you would be defeated by horror, discard St Hubert’s Key: immediately heal 2 horror’ means it has the added benefit of being a single use get out of jail free card so that even if you were on 2 sanity and about to die from taking 3 or 4 horror you could still survive with 2 sanity?

I suppose it depends on when you get those 2 horror healed but I think if a flashlight can never take a shroud value below zero it would be the same principle that your defeating horror can never take your sanity below zero. It seems to make more thematic sense this way and could make for some ‘miraculous’ play especially when fighting a boss for example, you could tank the damage for just long enough to buy your team another go round without anyone dying.