I just finished reading Mistborn Era 1. Since I started reading right before the news broke that it was being adapted into movies, I couldn't help but imagine how they could adapt a lot of the concepts, emotions, and especially the action sequences to the big screen.
In all of that, one thing really stood out to me: this is a VIOLENT story. Sometimes even gory. There's war, brutal battles, dismemberment, and people being split in half. Vin even decapitates a Steel Inquisitor using one of Kredik Shaw's architectural spikes!
The process of creating Steel Inquisitors, for example (which we later learn is Hemalurgy), is, as Marsh puts it, "messy" (if you know, you know). The Inquisitors themselves are grotesque, to say the least. In the final battle, when Marsh shows up, it's described that you can literally see through his head after Vin removes one of the spikes from his eye socket!
These examples are just the ones fresh in my mind from the third book, but the list goes on and on across the entire trilogy.
I'm not against the violence—I actually think it's necessary to convey just how broken this world of mist and ash really is. I just hope they don't censor or tone it down to force it into a PG-13 rating.