This is a pretty incredible card. Over 9 campaigns, you start to notice that the game often presents specific configurations of scenario mechanics that can all get bodied by a boot in the door:

• A scenario climax with one or two key locations, guarded by scary enemies or effects, that can be cleared by emptying out a high-shroud room (sometimes with a narrative shift or bonus for doing so instead of killing the enemies).
• Optional high-shroud challenge rooms with Victory 1 or Victory 2 attached.
• Rooms with incredibly high shroud values you can only hope to investigate by either following specific mechanics or making specific sacrifices (horror, card discards, clue expenditures).
• Needing to spend many clues for a certain effect, with a room that infinitely replenishes clues.
• Enemies or card effects tied to the shroud value of a room.
• New, in The Scarlet Keys: performing non- tests against a room's shroud value.

This is up there with First Watch in the vein of 'great Guardian utility cards your Fighter will struggle to squeeze 2-4 of into their deck'. And it's a level 0 event, so even the Tony brand of deck building can run it. You might think you specifically need high base to make it work, but almost any teammate wouldn't mind throwing one of their UCs in to the test. A good Mystic will reserve a Promise just for this; a good Rogue will wonder why Skeleton Key even exists.

Hello, I was wondering ...
Can you play or activate fast card between the actions of grappling hook? .

Some extra details for □□□ Impulse Control : If you start the game with 2x Honed Instinct at first, when you spend 3 XP to check the boxes, the 3rd copy can come in and replace any card in the deck for free, with the special customizable rule that came with the Investigator Expansion box (see below).

This rule also allow not including any Honed Instinct at first, then spend 3 XP (or more, like one of the □ customization) to swap in all 3x Honed Instinct with the customization into the deck at once. (e.g. If you think 3 cards deck space should be for something better than a base Honed Instinct.)

An investigator may directly purchase one or more copies of a new customizable card with one or more upgrades by spending only the amount of experience points required to purchase those upgrades. (Doing so counts as purchasing a new card, not upgrading an existing card.)

How good is this card in a regular build that doesn't include something like Lockpicks?

Let's do some math:

On Standard in The Innsmouth Conspiracy, there are 20 tokens in the bag to start. Let's assume that only +1, 0, and will trigger this (since you're trying to be at +2 for all checks). By my calculation, you have a:

• 36% chance if you make two tests per turn
• 48% chance if you make three tests per turn
• 59% chance if you make four tests per turn

I think assuming two tests is fair since you'll be using actions to Play and Move. You might also get tests during the Mythos Phase but you probably won't be at +2 for those checks. If we assume that the scenario is 15 turns long, you'll net 5.4 cards if you play it on turn 1 but only about 2.7 if you play it mid-game. That's not great. Preposterous Sketches will get you three cards immediately for the same cost and not take up your Accessory slot. Obviously, this card starts to look better if you can take more actions per turn (thanks to something like Leo De Luca) or if you routinely test at above +2.

There aren't a whole lot of good healing cards, and it doesn't seem worth 6 XP just to take some otherwise bad cards and make them good (you could just play the good cards to begin with). Still, this seems like it will get real value out of the occasional healing card that was already playable. Obviously this should be strong in Carolyn Fern and Vincent Lee. Some other examples for the not-healing-focused investigators:

• Book of Psalms was already a reliable blessing enabler with healing as a side effect. This will provide significant utility to a blessing deck.
• Hallowed Mirror is arguably the best dedicated healing card at 0xp. Soothing Melody doesn't cost any resources or cards; two healing for one action is actually a pretty good rate. This lets you benefit (maybe even more than normal!) when you don't have anything to heal.
• Empty Vessel, like most of these, heals you while also doing something powerful that you wanted anyway.
• Deny Existence, while expensive in terms of XP, was already one of the best dodges in the game. Again, a substantial improvement on something you weren't really playing for the healing.
• Lily Chen's Discipline. The active effect is already quite potent and reusable, and guardians can end up with periodic downtime to use it.

What most excites me about it, though, is that it might kind of bail out Shrewd Analysis. Two of the otherwise stronger Researched cards have healing upgrades which are basically duds (Ancient Stone and Strange Solution). Now, if you get one of those, you can spend some of the XP you saved with Shrewd Analysis to turn them into playable cards. All three Ancient Stone upgrades seem actively good now, and all four Strange Solution upgrades seem at least playable (Strange Solution is still obviously the best). I still don't think Shrewd Analysis is optimal, but I still like to see it get some indirect help since it's a lot of fun.