Good questions! Here's what I think.
1. If a Mistborn has the 'Tug Emotion' stunt for Zinc and the 'Push Emotion' stunt for Brass (which each give a +1 to Charm rolls), and is burning both, does the Mistborn gain a +2 to Charm? My intuition is yes, given that being able to burn both those metals in that subtle way should be able to benefit each other, but I wanted to be sure.
I'm a little torn here. On one hand, the player paid the advancements for the stunts. On the other, both mention the character subtly messing with the emotions of *everyone* around them, and I don't think the same effect should get stacked. For me, doing both at the same time would cancel the subtle
nature of the stunts and lose the extra charm die.
2. In a similar vein, if a Mistborn has the 'Steelrunning' stunt for Steel, the 'Ironslide' stunt for Iron, and the 'Extreme Speed' stunt for Pewter (which each allow the Allomancer to take 2 free steps without penalty), can the Mistborn move 6 steps for free in one beat? Again my intuition tells me yes, given that pushing off one's environment should only add to the speed already gained by pewter, and Ironslide isn't that dissimilar... certainly not dissimilar in a way that would detract from the other speed increases...
For me, they wouldn't stack. I might be convinced to add one additional step for some combination of them, but it had better have a really good narrative reason! Extreme Speed says the character moves around 40 mph; Steel and Iron mention moving objects at around 100 mph, and you have to be within 100 paces (Medium Range) to even detect what you want to interact with. (Further, with the right stunts.) They all provide the same benefit: moving two steps instead of one as part of another action, or three steps when going full tilt. I already don't usually allow stacking the same effect (see above), but in this case, I don't see how combining them could be faster. Steel or Iron have a higher limit for their respective speeds, but the effect is the same in game terms. Maybe if the Long Range and Increased Velocity stunts are also known? I'd also be a little worried about stopping after traveling at those speeds. Pewter could probably help with that, I suppose.
Basically, I figure it already allows moving a distance of up to 900 paces (from Sight to Long) while still retaining an action. What you suggest would be moving from Sight to Touch and still getting to act. As a combat beat is typically around 5-10 seconds, that sounds absolutely insane!
3. This one is to do with something mentioned in the Terris Supplement:
Terrisman’s Resolve (Terris only): Your Willpower permanently increases by 2, and you may recover Willpower during a Short or Long Breather without sitting the Breather out (see “Recovery” on page 189 of the Mistborn Adventure Game).Oookay, but there's nothing in the Recovery section that says you'd need to sit the breather out. If anything the text seems to imply that recovery happens automatically over those breathers[.]
Yep, looks like everything after the comma should be removed.