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.

After playing with this card for a while, there were some investigators that definitely had better uses with this card. Usually used in:

• Characters who can easily find Hyperphysical Shotcaster or recur it (= almost every ).
• Characters who would like some consistant fight/investigate option that their deckbuilding options doesn't support (= no , )
• Characters who can boost their primary stats through multiple ways

Notable examples that I found:

• "Ashcan" Pete: boost with St. Hubert's Key, Plucky. can use Duke to trigger Scavenging to recur Hyperphysical Shotcaster.
• William Yorick: boost with Beat Cop, Ace of Swords. Has innate recursion ability, can easily set up Scavenging with Short Supply + Yorick's ability
• Harvey Walters: boost with Dr. Milan Christopher or Whitton Greene, Death • XIII, Celaeno Fragments, Practice Makes Perfect. His innate draw engine allows him to find pieces more reliably.
• Rita Young: boost with Track Shoes, Peter Sylvestre, Fight or Flight. Has no access to rogue assets. Can recur Hyperphysical Shotcaster through Scavenging, and can get good burst damage with Dirty Fighting+Hyperphysical Shotcaster.

I think this might be an amazing card for Lola Hayes. The Hyperphysical Shotcaster is a neutral card, which means that Lola would be able to activate it regardless of the role she's currently in. It's also quite safe against her weakness (Crisis of Identity), so there is little chance the weapon would be discarded.

To piggyback on The Wall's extensive review, it must be pointed out how well the HPS works for Darrell himself.

The HPS as a weapon is really only useful for characters with low combat and willpower. If you can already fight, you have more efficient options. Compare to level-0 .45 Automatic; for 2 less XP you get +1 attack and the ability to reload it through other cards. The same goes for attack spells. That means the only characters that really want the Railshooter upgrade have high intellect or agility.

The main problem is, as it uses aether, only Ghastly Possession can reload it, and only for 2 shots even with the Aetheric Link upgrade (which increases the aether it comes into play with, not the uses value). And, if you have access to GP, you're probably better served by attack spells anyway. That means the only realistic way to reload it is to either dig it out of your discard or draw through your deck again, and either option is going to cost you a hefty $4.

Enter Darrill, who has no problem finding it with Whitton Greene, using Scavenging to bounce the empty gun back to his hand, and paying for it with Schoffner's Catalogue. He can even dual-wield it CQC-style with an Ice Pick. Being able to hit 3 damage in a single attack is a huge boost in efficiency, downing the majority of enemies in the game with a single action and significantly stretching your ammo.

Of course Minh has access to the same suite of cards with a slightly less focused stat spread, so it's really a matter of preference between them. For completion's sake I have to add that Minh could theoretically combine it with Gray's Anatomy to really stretch your ammo usage, but that's a whole pile of resources and XP on top, and you'd either need to evade or slap on an upgraded Raven Quill to avoid the opportunity attack. It's really not worth it.

Along with the previously mentioned Sleight of Hand, the two new cards from The Feast of Hemlock Vale: Task Force & Hand-Eye Coordination both give free uses without paying any cost of the Hyperphysical Shotcaster.