Due to the recently released ruling on "for each" and "for every" effects, Earthly Serenity can cause Carolyn to gain 1 resource per point of horror healed, turning this and the upgraded version into a pretty powerful economic card for her. I assume this is an experimental naturopathic remedy, which is why she can charge so much for it.

There are a lot of healing cards out there, and most aren't that great. Some, like Spirit of Humanity or Ancient Stone are at the top of the list because they can heal without a direct action cost to the player. Of the cards that convert clicks into raw healing, IME Earthly Serenity is probably the best of them.

Drop it for 2 resources for one action, blow up all 4 charges in a test for another, and ... that's it, you're done. It's a strong way to pull an ally out of the danger zone, fast. Compare to First Aid - play for 2, click 3 times, and ultimately heal one less. That said, it being a test complicates things: luck of the draw can have you fail to empty it in one go, although Mystics and Survivors easily have the to make that a rarity. And if you're running Hard or Expert tokens, drawing any symbol token can have consequences that easily outweigh 4 - or even 6 - healing in one action.

You'll probably pick it up mid-campaign when people are traumatized, but it gets good mileage - and the art is gorgeous.

This card really steps up in value when you play it with Dexter Drake. For 1 resource and 1 action, you can heal up to 4 damage/horror. Pretty powerful stuff. And then next turn you can throw it out for a Shrivelling and load up on horror all over again :D

If you have Showmanship down, you'll get a +2 to the test and be likely to spend all your charges in one go, even without any other Willpower boost.

This card does wonders with Akachi Onyele. Not only you get an extra charge, being able to take it back to your hand and play it again makes your party immortal. Suddenly you prefer to take damage yourself rather than your allies :D