Seceret Histories kills the theory, but I like the idea of a Scadrial character we know being Iyatil. So..SPOILERS. I'd like to think it's possible that she's Marasi. The mask comes from the third book of Era 2 Mistborn (after WoR) , in which we learn of the Southern Scadrians. Marasi finds and makes a connection with one of them and kind of hits it off , the fourth book hasn't come out, and I'm sure we'll see more of them, That being, she's one of the character than can be a world hopper, since her entire arch is finding her own destiny, and others already have a place in their world (maybe not wax, but he's not girl, so he's out). Also, Iyaltil seems to be, at least, one of the uppers of a very well organized group of researchers [investigators], and gang. Marasi would know a lot about how gangs work and how to run them, as well as researching the world around her, and the ghostbloods are very good at knowing things that no one else does. It may be out of her justice complex, but as we're seeing more and more, the cosmere character's moralities are getting stretched as the story progresses, so it's not unlikely that her justice is being shifted, considering the ghostbloods think they're saving the cosmere.
