Raven Wilder

I always figured Feruchemists could drain away as much of an attribute as they want so long as they've got room in their metalminds. They normally don't drain themselves all the way to zero, but if they did that with stuff like strength, breath, or healing they'd probably die (or at least pass out, and they can't fill a metalmind if they're unconscious).

I thought of an interesting combo I'm pretty sure no one's mentioned yet: Tin Misting/Iron Ferring. It's awfully situation specific, but I can think of a pretty neat use for these powers. First, the Twinborn drains their weight into their iron metalmind until they're almost weightless. Then they launch themselves into the air; maybe they strap themselves to a kite, get hurled from a catapult, or have a Coinshot Push them up. Anyway, thanks to their extremly low weight, they'll be able to go up really high and drift back to earth really slowly. And, while they're spending all that time up in the air, they can burn tin, letting them see everything for miles around in incredible detail. Cartographers would love them. Heck, it would be hilarious if a future novel set during Allow of Law times has a team of explorers out in the Roughs, and they've got a dozen Skimmer Ferrings bobbing around in the air, drawing maps of what they see, while a bunch of Coinshots run around on the ground using Pushes to keep them from falling. P.S. As for how future novels could have Mistborn in them, I got two words for you: genetic engineering.