Look at City of Archives...

"Body of a Yithian: During the setup for this scenario, each investigator is instructed to replace their investigator card with one of the Body of a Yithian investigator cards."

and then:

"Each investigator’s deck remains the same, but for the duration of this scenario, they must use a Body of a Yithian investigator card, and therefore cannot use any of their investigator’s abilities."

Does this card potentially break the scenario? Can you choose an investigator, with a normal stat line, that comes close to your original investigator or better suits your deck?

I always want to take this card, but what kills it for me is that third slot. That's a big ask for something that tends to be situational. I think this card was designed with higher player counts in mind. It's meant for a support investigator to back up your combat investigator. In that role it's pretty versatile and you can probably justify filling almost half your slots with it.

Not in one or two player. In two player you need to be able to fight or investigate reliably and with this thing hogging your best slots you're not doing either. It's worse in solo where you need to be able to do both. Those three slots make it useless as a backup or utility weapon. Maybe you could pull off using a combat spell along side this, but that's all you'll be doing. You better hope you already have a high book stat.

Thinking of ways I might improve this card; remove the exhaust requirement, have all shots spend a charge, and boost the number of charges. Alternatively, have it give you a passive boost to face and foot instead of giving it to you during the attack.

This card is really good for Patrice Hathaway seeing as it combos with Patrice's Violin to allow her to make 2 resources or a card and a resource out of what would be a dead draw. The +1 Int is a nice bonus is you're building a cluever deck, and it's backup soak in case you get jumpscared by Watcher from Another Dimension.

Awesome card for Mandy Thompson!

If you have her in your starting hand you get to trigger Mandy's reaction ability and essentially get 2 tarots for free!

Oh, wait...

Jokes aside, still a good pick in Mandy, as you don't have to trigger Anna's reaction after she enters play and can call herself later after the weakness has been dealt with.

This card is pretty insane, as you get to staple the effect of any level 0 asset or event to a successful skill test at no cost, along with an unexpected courage to help you with that test. As of printing, here's the valid users - Sefina Rousseau, Zoey Samaras, Father Mateo, Sister Mary, Luke Robinson, Lucius Galloway, Agnes Baker, Akachi Onyele, Marie Lambeau, Dexter Drake

Here's a list of some of the generically powerful things you can do with it, even without specific scenario/card combo interactions. "At no cost" is an insane line of text that makes it very powerful with any of the doubles from Hemlock Vale. This is just my list that I threw together, I'm sure there are other respectable cards and some that are particularly strong given specific scenarios/situations. To me the thing that makes this card sing is its sheer versatility - almost any of the below effects are very strong, and you get to choose the best one for any given situation.

Gain 8 Resources for investigators at your location: Bank Job (Hot Streak is 4xp and nets you 7 resources)

Draw 5 Cards for investigators at your location: Thorough Inquiry (All In is also 5xp, but Memories doesn't have the weakness clause)

Get an automatically successful +1 damage fight(You don't take the attack, as the enemy attack is a cost): Toe to Toe

Take an extra action every turn for the rest of the scenario: Leo De Luca

Discover 2 clues: Extensive Research

Move, discover a clue, and activate an asset (can also be given to other investigators at your location): Task Force

Deal 3 damage to each enemy (and investigator) at your location or a connecting location: Dynamite Blast

Automatically evade or deal 1 damage to all non-elite enemies at your location and connecting locations: Elaborate Distraction

Evade all enemies at your location (including elites): Cunning Distraction

Move up to 3 times without engaging enemies: Scout Ahead

Get a generically powerful yellow card: Dr. Milan Christopher

Get a generically powerful green card: Lucky Cigarette Case

And some situationally useful ones:

Gain 3 slotless horror soak for your team: Something Worth Fighting For

Gain 3 slotless health soak for your team: True Grit

Resign: "I'm outta here!"

Gain 3 supplies or ammo for assets you control: Cleaning Kit, or with soak if you have an ally slot: Venturer

Double the ammo or supplies on an asset you control: Contraband

Turn your events into skills(with no weakness, again, additional cost is removed): Crystallizer of Dreams

Grab a clue and find an enemy to kill: Kicking the Hornet's Nest

Discard a Terror treachery from an allied threat area (as long as you have at least 1 clue): Logical Reasoning

Grab any one of the masks: Cat, Fox, Mouse, Sparrow, Wolf

Trade resources, items and allies: Teamwork