[SPOILER] Plot Discussion Thread *Spoiler Alert*

[Kein]

Wait a gosh-darn minute....

How is Mandus not marked by the shadow if he touched the orb?(And to some extent, abusing it's power?)

Also, how much do we know about the engineer? I can only remember one reference to him, and that's a conversation between the professor and Mandus, where the Engineer is fully on-board and "has seen the evils of society" to heavily paraphrase? I'm assuming he's the guy who designed the machine?

http://amnesia.wikia.com/wiki/The_Shadow

The Shadow is the mysterious guardian of the Orbs, hunting down and killing anyone unable to fully take control of the Orb


So, obviously, Mandus is able to fully take control.

No, he doesn't. Weyer and Alexander could, Mandus had no willpower and mental strength.
Also:

That's one of my main reasons for believing that Mandus didn't find an orb but something...else. In a note, Mandus explicitly calls the orb used in Brennenburg The Orb, and is aware of the power that orbs can possess. But he never says the word orb again. He only refers to his Stone Egg and there's never a single mention or description of the Shadow, which I take to mean that this was something other than an orb, but perhaps related to it. Justine had the Soapstone that drove her insane and gave her knowledge of the orbs, maybe Mandus came across another, different kind of stone in this array of supernatural objects.

Wait a gosh-darn minute....
How is Mandus not marked by the shadow if he touched the orb?(And to some extent, abusing it's power?)

We have no idea yet. The in-game resources hints that it is may be orb indeed, but it does not work the same way as Orb so it could be something different.