How to understand (Max once per game)? You can heal an investigator only until you fail, or you just cannot take more than one trauma per game once you fail the test? Or maybe you can heal any investigator max once per game and if you fail you get trauma?

Not much to say about this card, except I like how it is very close to the Heavy Rain treachery in Scarlet Keys, so we have consistent rain mechanics.

The reason I am writing this is a maybe helpful suggestion: I was going into the mines on day 2, and I didn't like the flavor of rain underground. In case this comes up for you and you feel the same, and you own The Forgotten Age (as you should), in the encounter set Forgotten Ruin, there are 3 copies of Deep Dark. I am switching these out for this scenario on Day 2. They are not identical, but they both target your clues in a way. Deep Dark seems weaker, but it's a good flavor fit I think. In 4 player, Deep Dark could be worse if it comes up at the wrong time.

So they do buffed .45 Automatic by reducing 1 resource, which is okay. But also with a new name, like why? I don't really see a problem if they just buff .45 Automatic instead.

I don't really appreciate card games eliminating old cards like this, although I can see .45 Automatic are not eliminated totally in Arkham, because you can take them both if you need four .45 Automatic. But still, this gun will replace .45 Automatic completely.

Fantastic ally on Leo Anderson, given it synergises well with his main ability

Main issue Leo has, is that eventually you run out of space for allies, which basically blanks your ability outside replacing allies with other allies, but with G-Men as long as you keep a free slot for them you can playing them using Leo reaction and enjoy a 2/2 tanking (or possibly more with The Star) and +1 to all your stats for a turn as long as you have one resource, which will get refunded during upkeep.

Just don't let them get defeated! I don't think the forced effect will trigger from the discard pile!

The new core doesn't offer a lot of skills for Silas, and this might be one of the more dangerous. Every time you apply it, you're risking 20% of your sanity. Then again, with the limited weapon pool, this is an excellent partner to meat cleaver. Take a risk on another check and then calm yourself with a crowd-pleasing ghoul decapitation. What Mystics like, especially when the Jim Culver ally's in play, is you can commit this for others and gain the "benefit" yourself. Agnes's ability is gated to once per phase, but this is a perfect way to deal damage to a foe in Mythos. And it's even a spell, which means Arcane initiate can fetch this for you.