Elend Sees the Mist Spirit
Elend really does have a lot of faith in Vin, even if he doesn't worship her. He ascribes an almost supernatural power to her. And, I can kind of see why he would. In these books, Vin's almost less of a character and more a force. Like Ruin and Preservation, in a way.
Regardless, this chapter is about Elend giving up—then finding his hope again. I bring the mist spirit back here for a final appearance, but I wanted to be careful not to have it give too much information to Elend. Not because I don't want the information itself to get out, but because the mist spirit hasn't been a presence in this book, and so I haven't foreshadowed it enough. Therefore, if it simply showed up and gave a bunch of answers, I think that would feel cheap to the reader.
The mist spirit is, as the next epigraph explains, the remnants of Preservation's mind. I don't delve into it too much in this book, even the epigraphs, but Preservation's consciousness is indeed separate from his power. However, his consciousness itself has a limited power. And that is what he used to bind Ruin.
That did not weaken his power, which still protects the world. Instead, it cost him his mind, leaving behind only a faint shadow—like the mists' memory of Preservation, far removed from what he had once been.
That consciousness attached to Preservation—like the one attached to Ruin—is a part of Adonalsium, which will eventually be explained. Suffice it to say that in a pinch, Preservation could draw upon the power of his own mind and use it to imprison Ruin. This was why he was able to pull of the trick, as Ruin wasn't expecting it. He might have anticipated an attack using Preservation's power, but not his mind—not knowing what burning his own mind would do.
That is why Preservation's cage captured Ruin's own mind, but not his power.