I'm going to agree with the previous poster--the Unspeakable Trio are certainly top contenders for worst weaknesses in the game, particularly Bloodthirsty and Unspeakable Oath (Cowardice). If you happen to draw one into a deck that is set up for it, great, but obviously I'm not talking about that.

What makes them so bad? Perhaps we're supposed to say they are boring, because it's considered bad form to complain about difficulty ("Don't play arkham if you don't want a challenge!" There, I've said it for you, so now you don't need to comment.). However, I don't think they are boring. I think they are frustrating and demoralizing in a way that I consider bad game design. They can be extremely resource intensive to manage, requiring expending resources and time to draw and play special cards to handle the thing and to take the actions required, which are tests you have to actually succeed at to finally discard the dang thing. So, they are disproportionatly difficult in terms of investment compared to weaknesses that require just spending two actions and being done. But there's a lot of unevenness in the weaknesses-- Paranoia and Amnesia are also pretty brutal.

These get moved to the "bad design" category for me because they are directly destructive to the main mechanism of player engagement with the game: deck building.

As the poster above noted, as an unlucky draw, you have to redesign your deck around these. Chances are good you've invested a lot of time into designing your deck, because that's your main opportunity for choice, control, and experimentation. It's your place to "shine." It's also the place you get to decide what kind of character you play. When a player has chosen to play an all-fight tank with agility 1 or 2 and they suddenly have to be able to evade a monster twice in one turn, you've taken away their choice about what kind of game experience and fantasy they get to have. The player is forced to clog their deck with stuff to deal with the weakness, perhaps significantly compromising their build.

If you were the dungeon master for a game where your player was super excited to play a wizard, and you consistently targeted them with challenges of physical strength, you would be a bad DM. That's what this is. It's major side quest in every single scenario for a character type you didn't want to play.

And what's the consequence of failure? You hit them in the deck AGAIN, preventing the player from enjoying the rewards of a hard fight by depriving them of XP to upgrade their deck. Now you've made their game harder, their character lamer, and they are falling behind the rest of the team in capability. Removing the reward for a TEAM success and generating a feelings of envy and disconnect, is simply bad design in a cooperative game, especially since no one else can help you with these cards.

"So just house rule them." Thanks, I will. I was just annoyed enough by the card design that I wanted to actually post an analysis of why I think they are bad cards.

You can win this card in War of the outer gods. There is almost no reason to not include it in your deck. Works best for investigators that want to avoid monsters and have other stuff to do (Seekers?) Very cheap, 4 free monster evasions.

I got this card and put it in Daisy Walker's deck. It was amazing. She could just travel around, ignore the enemies and do her thing.

I think it would fit in nearly anyone's deck, the body slot is not that much used.

This is not bad in a curse Amanda Sharpe deck.
Challenge 1, get the original grimoire translated. Tempt Fate helps, Promise of Power as your under card helps, Deep Knowledge helps... I have played a few times with an Amanda Deck (published) that has seen the grimoire translated in 75% of scenario 1.

Challenge 2, get secrets on it to make it work. Truth from Fiction helps, Enrapture as an under card helps, Eldritch Sophist helps, Favor of the Moon on your previous Tempt Fates helps... In the games that I have played with a translated grimoire, I have gotten use out of it at least once every game, most games twice, but rarely 3 times.

It is expensive, but I have a successful character (at least on normal) Amanda is still strong despite playing this strategy. Fey works nicely here as an under card, save the Favor of the Moon play for the last skill test and return it to your hand. Rinse and repeat until the favor is gone. Gaze of Ouraxsh can be great if you need some punch.

TLDR: This card in a Leo Anderson deck is an absolute tank. Include it if you want to have an easy time on hard/expert mode.

I should mention this isn't much different than the review done by MiskatonicFrosh but I just felt the need to include my review of this specifically with Leo Anderson.

First off, this card on its own provides you with a heal for damage and horror and then soaks one damage and horror for 1 action and 2 resources. Compare this to First Aid, liquid courage, etc. All that can be for action costly healing assets. The big benefit of those compared to this card is they dont take up a valuable ally slot.

In walks Leo Anderson and his armada of ally's. I should say even with Mitch Brown, I upgraded to Charisma to have an extra slot and I'm only half way through my campaign, but Medical Student is just a must add for Leo's deck. I have had this situation occur in two straight situations:

Have already taken some damage/horror from encounter deck/enemies. Play the Medical Student and heal myself 1/1 as an actionless cost. Play calling in favors to pick up another ally (guard dog or even one time I picked up ANOTHER medical student) and then play that card at reduced cost. Then with Survival Knife armed and ready, I felt comfortable going into fighting a big boss. I used my Cyclopean Hammer for one swing. Then on the enemy phase, I absorb the hit with guard dog/medical student and fight back with my knife. Next turn begins and I still have the Medical Student I picked up from the previous round and play it again as an actionless cost to heal myself. I should note that in order to play calling in favors, i didn't let the medical student absorb any hits, I only sacrificed them the second time around when I played them, but got the bonus healing of 1/1.

What did this all cost? 1 action and 4 resources (to play calling in favors is the action and one extra resource to pay for guard dog) to heal/soak up a total of 6 damage and 4 horror. Not to mention with survival knife and guard dog, you have a solid tempo of attacking/doing damage during your phase and enemy phase. In terms of cost benefit this card is just broken for Leo.

This is the most effective and fun way to heal. I didn't really need Mitch Brown, but Leos special effect is what makes this work so well. I can't imagine a deck of his without this card. I should also mention I try to avoid running the same ally's. So for example I wont run Leo De Luca with Leo even though they are perfect for each other because I just like the variety.

The last thing we need to consider though is a moral or philosophical one that the game developers might not have considered. Should the investigators of Arkham be using Medical Students of Miskatonic University as cannon fodder for the monsters of the world? I'll let the comments decide.

As I understand (corect me if I'm wrong). Case study

Start of investigation phase. Sefina Rousseau plays Black Market. There are Pilfer and Backstab among those cards.

It is the turn of Rita Young. She can play this card and she does! Every time she does it, she hits the target and finds the clue, she even passes by 2 or more every time.

In accordance with the "pass by effect", the played cards return to... Sefina Rousseau's hand in the end of Sefina's turn (which may take place next round if this round Sefina had her turn before Rita)? As I understand, they do.

As per my interpretation of rules, in this case the word "you/your" refers to the one who controls the card. Even though Rita can play it as if it is in her hand, the cards are still considered to be controlled by Sefina.