You were probably expecting Marsh’s return–at least, you probably were when you read the chapter where he ‘died.’ Making Inquisitors via Hemalurgy requires killing other people (see book three for an explanation of the process) so there’s a lot of mess involved.
Anyway, I planned for his return here. I wish, again, I could have done more with him. There was another whole book going on with him being watched by the Inquisitors–him thinking that he’d earned their suspicion when they were really just impressed with him and planning to make him one of them. That’s how it usually works with Inquisitors–they grab a new recruit, usually an older one, and ‘draft’ him into their ranks before one of the other Cantons has a chance to corrupt him too much. So, they were looking to make another Inquisitor, and Marsh happened to be the most promising recruit training in Luthadel at the time.
He never understood how far his infiltration would take him, or what it would end up costing him. The payoff is that he figured out how to kill Inquisitors–they were all built to have a weakness, so that the Lord Ruler would have power over them if he needed it. Pull out the right spike, and they come tumbling down.
Marsh’s plan to kill the Lord Ruler is a good one too. Unfortunately, the Lord Ruler’s power doesn’t come only from Hemalurgy, but from other things as well. If he’d pulled off the bracelets instead. . . .
By the way, the mists getting pushed away from Vin and Kar here is a clue of some sorts. Inquisitors push away the mists, rather than attracting them, when they use their powers. I’ll explain this in book three too.
Two attributes that can be stored up by Feruchemists, by the way, are healing and the ability to move very quickly. The Lord Ruler had access to both of these abilities in extreme, augmented ways, which was part of what has made him so powerful. More on THIS sort of thing in book two.