distinctly remembering the idea that having metal on you while facing them was a bad idea. any idea why?
The major issue would be that if you have metal on you, a Mistborn (like Vin) could manipulate it (e.g. pull you towards her, yank it away from you, push you away, etc.). A normal person who has a knife in their hand would just be asking to get it shoved in their face, essentially. There are some rules to the manipulation of metal on a person, though. For instance, it isn't possible in most circumstances to manipulate metal that has been ingested or is inside someone in another way (for instance, a piercing) except in certain circumstances that I think for the purposes of one of these fights would be considered unrepeatable.
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"Luxe, calme et volupte." - Charles Baudelaire, The Invitation to the Voyage