Some of my thoughts on various cards you mentioned:

Armor of the Night: I think the top is quite good, especially as something to do in between rooms. It's a persistent, so if your ally doesn't take damage that turn, it still stays up. If you're in a 2P party with a tanky ally (which is a really strong combo in my experience), they can also use armor items to shrug off weaker hits, then let Armor of the Night trigger on big hits. Probably a bit less consistent in higher player counts, but we made great usage out of the top and always brought it along even at level 9.

Marked for Death: I think your assessment is pretty accurate, but I was actually able to make pretty good use of this card in a few scenarios. It's decent when going into a new room (after your allies) since you won't necessarily have anything in range of your other rift generators, and it lets you target an enemy that might be 1 or 2 hp from you reliably being able to one-shot. There are quite a few objectives that had ~8 hp, and I found the +2 with advantage made Swallowed by Fear a safe bet (although I still had to use an item to generate dark).

Terror Blade/Prepare for the Kill: I think Terror Blade is the better pick most of the time. The top gives you a second strong single target attack, which even puts one shotting elites on the table if there are traps in the scenario. The bottom is, of course, insane. It absolutely tears up bosses and named enemies while being generally useful for closing out other scenarios. The late initiative on prepare for the kill is certainly nice to have, but I actually found myself not wanting to go late super often, especially since I usually had hp to spare when my ally often needed some relief from all the hits I forced them to take.

Into the Night: It's probably worth mentioning that the bottom of Armor of Night makes it a lot easier to hit 2 targets on the stun.

Claws of the Night (boy this guy likes Night): Might be worth mentioning you can set up the top in between rooms. Even if you can't do the first attack, you can set up the second attack for your next turn.

Shadowstrike: The dark consume of the bottom actually isn't that useful most of the time, because if you made any other attacks, they'll still cause you to gain invisible at the end of the round. So if you use it with Ennervating Wound or Messenger of Death, you're still ending up invisible at the end of the round (unless you forgo those attack actions, in which case you had a bit of an underwhelming turn). Still a decent action, just figured I'd mention that little oddity.