Writing up some notes for a game of HW I'm hoping to run or play, since I've got some interested players. I'm filling in gaps and homebrewing from the Forged in the Dark SRD. Currently breaking my brain on the Revisionist preview you posted earlier, since I'm excited about that crew type:
1. Inversion Lab: "Retroactively plant items in Archives."
My current interpretation: I have to be able to fit a "host object" into the lab. For example, I could put a briefcase full of documents in the lab and plant a weapon in the Archives so that I could Restore the briefcase to get the weapon out. How I'm thinking it'd play out at the table:
Player: "I'm carrying a briefcase full of documents in through the front door."
GM: "Security checks the briefcase for weapons."
Player: "That's fine. There aren't any weapons currently in there."
Player, later in the score: "I do a flashback where I brought along a ping rifle in the briefcase."
GM: "You're going to need to explain why the guards didn't find it."
Player: "I prepared to be searched by using the Inversion Lab. I put the briefcase in the wayback machine and added the rifle to its history in the Archives. I want to roll Restore to 'revert' the briefcase to the state where it contained the rifle I planted. The rifle wasn't there when the guards did the search."
GM: "That makes sense. You don't need to take any stress for the flashback, since it was a reasonable preparation. Roll Restore to see if you can retrieve the rifle."
Without the inversion lab, I'd probably have to pay more stress or have a better explanation of how I got the rifle in there undetected.
2. Memory Tomb: "+1d to Find and Restore on Site"
I'm guessing it's referring to such checks made inside the "Tomb."
3. Inversion Mastery: "Change the past with a Score"
This one just scares me, but at least it'll take a while before my crew would be able to get it. I'm just going to guess there's a much longer explanation than would fit inside the circle. Of course, it could just be fun having the crew fight cyber-Cthulhu as they do literal time travel by going into the Archives.
4. Message In A Bottle: "When you indulge [Futuresight] by describing an unforeseen complication that will soon affect the whole crew, you may clear 1 additional stress. Also a Mysterious Stranger will assist any one function roll you make - from now until you next indulge this recall."
Mechanically, this is easy for me to understand. It's not so easy for me to get what's going on from a narrative perspective. Is the Mysterious Stranger like your future self hitting World's "rewind almost everything" button and helping you out in the new timeline that results? That's the closest I can imagine without involving "actual" time travel.
5. Stable Loops: While paying the costs of any flashback, you may mark Memory as if it were stress. How do you close the loop?
Mechanically simple, but still confuses me on a narrative level. I'm kind of guessing that from a narrative perspective the Memory expense represents manually changing the past to accomplish the same meta-effect as a flashback.
In some of these cases, I'm just kind of tempted to say, "It's Archive Magic, let's not try to explain it and just get on with the game."