This is actually a pretty nice perk line, but it has a problem. It buffs a skill that, at the time of this writing is not very useful for the high level game. The real problem is that there just aren't any valid Shadowlands weapons that can sneak attack. Enhanced Mantis Scissors are the closest we have, and are clearly not a valid SL option. That said, this perk line adds a fairly significant amount to sneak attack as well as providing a perk action that adds another 100 to sneak attack temporarily.

Shadow Stab, the first perk action, is a direct damage perk action that requires you to be behind the mob when executing it. In my experience, you'll get a hit for around 650 damage (tested at ~level 202).

Blade of Night is a sneak attack buff (+100) that actually does help quite a bit if you are actually using sneak attack and backstab. This is a perk action that I look forward to training again once there are valid SL weapons in the game.

Shadow Killer is the least useful of the 3 as it requires some precise timing and some sheer luck. To execute this very generous (2469-4585) direct damage perk action, you need to have "Blade of Night" running on yourself and "Chemical Blindness" running on the mob. The real problem is that "Chemical Blindness" is not an Adventurer perk. It is Doctor, Engineer and Trader only, and comes in the "Alchemy" line. This is a line that boosts chemistry and pharmaceuticals. So, not only do you have to time "Blade of Night" correctly, but you have to get the Trader/Engineer/Doctor in your team to run their perk action on the mob. Oh, and you have to be behind the mob too ;)