Warning: The following text will contain spoilers for the end of Mark of the Ninja. This probably should be expected for the final episode of a lets play of the game. But given what I am going to talk about is revealed in the last 5 minutes or so I think a spoiler warning is only fair.
I definitely did not see the twist here coming. That Azai was betraying us and something fishy was going on sure, that was pretty obvious, but that our companion was a mark based hallucination was a total surprise. It is the kind of thing that makes me want to go back and see if anyone interacts with her in cutscenes.
I never thought it odd that she always was capable of catching up but never attacked foes for me, because she is an NPC in a game, clearly intended to be a guide character. So that she never helped directly was unsurprising, heck one of the level puzzles revolved around actually helping her get past an obstacle. Something that theoretically was totally unnecessary.
Ultimately I sided with my hallucination not because it was the right thing to do, honestly I am very sympathetic to Azai and his plan to allow the clan to continue. But at this point I figured Mark was completely under the Mark's delusions, after all just how many clan members did he kill to confront Azai? And not just the well equipped stalkers. All of the guards on these levels turn out to be regular ninjas after you kill them and I have no idea how much of a threat they really represented. If I do side with Azai I think I would have to have taken a pacifism based approach to the last level.
I had a great time with Mark of the Ninja, while the keyboard and mouse controls are occasionally frustrating, the light, shadow and noise systems work so well and it is really satisfying working out how to get past a set of guards either through slowly whittling down their numbers or just passing by while they are unaware.
Ultimately I wish I had gotten around to playing this game earlier, when more of my friends were playing it.