Here is the Silas Marsh deck that I used during my playthrough of The Return to The Night of the Zealot campaign on YouTube. Here are the links:
https://youtu.be/dRlsGRWXeI0 - Return to The Gathering
https://youtu.be/jamYCGShjqI - Return to The Midnight Masks
https://youtu.be/aiAxTB6BwXg - Return to The Devourer Below
The deck is based on a deck entitled Call of the Sea by Trilkin. I made a few changes to Trilkin's build, removing Eureka and Last Chance to make room for True Understanding, which worked extremely well, and Hiding Spot. Hiding Spot is in the deck solely for The Devourer Below. You can drop it on the Main Path before you advance the Act and then slip past all the Cultists to the Ritual Site. As long as none of those Cultists are hunters, you're golden. If you're not playing The Devourer Below, I'd replace Hiding Spot in a heartbeat.
Return to The Night of the Zealot is a very short campaign, so it's difficult to get a good feel for the upgrades. Peter Sylvestre (2) is the most obvious upgrade, and he was amazing in The Devourer Below. Try and Try Again (2) seemed like a good choice, but it never hit the table in either The Midnight Masks or The Devourer Below. Flare and Stroke of Luck both earned their keep in the final scenario. I had once experience point left over, but I wasn't sure what to spend it on. If I had earned at least one more XP, I would have upgraded Lucky! I also had my eye on A Test of Will. I believe the only other skill you can upgrade is Deflection. I've seen Deflection (2) do some good work, so it's certainly an option to consider.
I really enjoyed playing this deck. It feels extremely tight, and I had a lot of trouble deciding which cards to take out. Silas' response and Elder Sign ability are fantastic. I really liked the addition of 'Not without a fight!' The ability to commit it to a skill test against a big enemy, pull it back to your hand if you don't need the icons, and then commit it to the next skill test against the same enemy is so good.
I was worried at the start of the campaign that Silas may not have enough Intellect to investigate effectively, but Perception, True Understanding, Lucky! and 'Look what I found!' proved to be just enough. Don't forget that you can use Silas' ability to pull a skill card back to your hand to fail a skill test so you can play 'Look what I found!' That saved my ass in The Devourer Below.
I toyed with the idea of adding Newspaper (2) but, again, I couldn't decide what to remove because the deck seemed to function so well. Kudos to Trilkin for the design.
I was intrigued by the idea of adding Hemispheric Map to the deck, since it boosts both of Silas' weak stats. Theoretically, it's strong in The Midnight Masks. Unfortunately, it's not great in The Devourer Below, so I left it in the box.
As I said, I've really enjoyed playing Silas. His abilities are very powerful and he can handle himself in a fight. Silas' sanity is quite low, however. I wasn't too worried about it during this campaign. If you're playing a campaign such as The Path to Carcosa, which puts a lot more pressure on an investigator's sanity pool, make sure you include more protection, such as Cherished Keepsake, which was in Triklin's build. I removed it for Fine Clothes, then removed the Fine Clothes and forgot to put the Cherished Keepsake back in.