In my opinion, Hyperphysical Shotcaster is the best card in the Scarlet Keys investigator expansion. Better even than Darrell Simmons: for he is but one man, while this card improves many.

I do not particularly condone taking this card for 0 experience when because you can buy customizable cards with their upgrades without paying the 1 xp "new card" tax (as per the rules insert); although I do not hate taking a copy in the first scenario of a campaign if you're planning to Refine it. At least you can chuck it to an Act of Desperation or something.

Shotcaster obviously lives or dies by its upgrades. No other card interacts directly with aether so its uses are limited. Before I get on to the upgrades, however, its excellent collection of key words give some fantastic synergy that is worth considering as we explore further (not considering encounter cards):

Item:

• Sleight of Hand grants extra uses that turn, just be sure when using the mutated Taboo to not to spend more than 6xp on the Shotcaster (making it level 3). Amazing for Gloria Goldberg, Mandy Thompson, Rita Young, and most rogues.
• Act of Desperation with this is pretty good for William Yorick.
• Jury-Rig and Reliable buff skill tests. Well-Maintained (1) returns it and other upgrades to hand when it runs out of aether, and is the guardian equivalent of Sleight of Hand.
• Backpack (0 and 2) and Tetsuo Mori tutor for it.
• Tetsuo Mori, Professor William Webb (0 and 2), Scavenging (2), and Salvage (0 and 2) return it from discard. Specifically Scavenging (2) is pretty broken here with Telescanner as it can return itself to play immediately and potentially never run out of aether.
• Bob Jenkins, Charles Ross, Esq., and Schoffner's Catalogue help pay for it.
• Joey "The Rat" Vigil (0 and 3) makes it fast and (3) can sell it early.
• "I'll take that!", Teamwork, and Untimely Transaction can share it with another investigator (helpful since it is unique).

Relic:

• Antiquary helps pay for it, and buffs all its skill checks.
• Dr. Elli Horowitz and Whitton Greene (0 and 2) tutor for it, and it lets Whitton buff your stats.

Weapon:

• Bandolier (0 and 2) give extra hand slots when holding it.
• Enchant Weapon (3) makes Railshooter more potent.
• Prepared for the Worst (0 and 2) and Randall Cho tutor for it.

Firearm:

• Bruiser helps pay for it, and buffs all its skill checks.
• Custom Modifications, Marksmanship (1), and Snipe (1) can buff Railshooter.
• Quickdraw Holster (4) gives another option to juggle hand slots.

So with all this support available from merely the keywords, which investigators can benefit most from each customization? I'm glad you asked, hypothetical straw man.

Railshooter (2xp):
Excellent way to give a fight option to characters that did not have many good ones, although fighting is not the only means of enemy management. Every single mystic can take this instead of a fight spell to save precious arcane slots. Rogues with high get fights that are as good as their evades. Seekers can use this to supplement or replace their limited fight tricks such as "I've got a plan!". Some survivors, such as "Ashcan" Pete, appreciate backup fight options.

Telescanner (2xp):
Many characters suck in solo play because they just cannot reliably pick up the clues that are needed to win the game. This is the upgrade that fixes all that. For some characters it might be the best thing to spend the xp from In the Thick of It, especially those who can afford chicken soup to mitigate the trauma. Mystics get less utility here than for Railshooter because Sixth Sense exists. Survivors have even more utility because of the potentially broken interaction with Scavenging (2).
So here is every single character for whom I would seriously consider taking using their very first 2xp: "Ashcan" Pete, Daniela Reyes, Kymani Jones, Lily Chen, Mark Harrigan, Nathaniel Cho, Rita Young, Silas Marsh, Stella Clark, Tony Morgan, William Yorick, Winifred Habbamock, Zoey Samaras.

Translocator (2xp):
Lets your Shotcaster do a fair impersonation of Bait and Switch or Survival Instinct. Decent repeated enemy management, especially for enemies without the hunter keyword, although it does not affect Elite enemies. This is also action compression which is good for tempo. Zoey Samaras can even use this to evade one enemy and drag in another from a nearby location, scooping up more resources and triggering Zoey's Cross on each of them. I also like this upgrade for investigators that really struggle to evade and don't have many options to do so, such as Norman Withers and especially Harvey Walters or Vincent Lee.

Realitycollapser (2xp):
It's like A Test of Will (0) and Alter Fate (1) had a baby. This is an amazing upgrade that will fly under the radar for many, but is absolutely clutch in so many situations. The only problem will be juggling the forms of your Shotcaster (unless you can ready it as "Ashcan" Pete).
To be clear: if you can pass the test consistently, then this upgrade is amazing for nearly every character in the game (except Carolyn Fern who can't take it).

Matterweaver (2xp):
With so many other good upgrades, I can't in good conscience recommend spending experience to allow a 4 resource item to pay for more items. Schoffner's Catalogue and Hot Streak do this better, but if you're using this to jam Agency Backup four times then more power to you.

Aetheric Link (4xp):
Getting two extra aether is not a bad use of 4xp if this is going to be your main form of clue gathering or enemy management. Survivors take Scavenging (2) instead, guardians can grab Well-Maintained (1) for cheaper, and rogues might just stick with Sleight of Hand. Its not bad if you definitely want a second manifest ability on your Shotcaster; i.e. if you rely on Telescanner but would also like Realitycollapser, then this gets much better.

Empowered Configuration (4xp):
+2 skill value when you are already using your best skill to start obviously sounds great... but Antiquary and Bruiser are less experience, do the same thing and more, and all five classes can take at least one. The other problem is that most characters that use the Shotcaster will be doing so to cover a gap in their arsenal, so the longevity of Aetheric Link is probably better and the more unique effect. Save your experience and get more copies of the talents.

I guess this weakness has a great potential to be misinterpreted. I'm even not sure I'm getting it correctly. How I read it:

During each Carson's turn of each investigation phase he has to commit a card to an action of another investigator. It means that this card can only be committed to an action that was granted to another investigator by Carson himself. Well, some other scenarios should also work (e.g. Carson takes Liquid Courage with Versatile and heals his teammate), but they are less likely to happen. Doesn't help to commit a card during this investigation phase when it was a turn of another investigator.

It shouldn't also work when you committed a card withing an action granted by The Stars Are Right or At a Crossroads.

All the class specific weaknesses from this expansion have obvious links to strengths or specific archetypes of that class. Underprepared seems like the worst of them by far, because this is the most focused of the cycle and Survivor have diversified their archetypes.

Almost all Guardians can fight, all Seekers can draw cards, all Rogues can gain resources/actions, all Mystics use their arcane slots. But not every Survivor plays anything resembling the super low to the ground style required for this card.

Overall I really dislike the design of this card due to the variance in effect. If you are Patrice with double Cornered this card is a joke but for any midrange investigator this card is worse than Amnesia and Paranoia on a single card.

After six years, the guard dog finally got an upgrade, and it is a doozy. An additional hit point and sanity is great, making this even better to pair with cards that buff allies. But the new ability is the star of the show: a zero cost engage & an attack that triggers the dog’s ability. In single-player, that’s not very useful, But in multiplayer, it lets you change the order of operations. Grab an enemy off the seeker, letting them complete their full turn instead of flailing around with evades. Engage and chew up a whippoorwill.

Combo pieces worth considering: hunter’s armor, survival knife (0 and 2), The star 17, bandages, Aquinnah (either).

Not a review, but a question: Does this card work with player effects like Lone Wolf? Seems like it has immense potential. Would love to include it in big money decks. Has anyone found a lot of success with it?