breadcrumbs

So the real question is where do Soulcasting fabrials come from? Obviously it's not enough to create a copy and fill it with gems, as the Davars have shown us. What special aspect about their fabrials allow them to Soulcast, and if it does at all, how does it interact with Shadesmar?

As I recall, the envisagers tried to put themselves in harms way in order to force a manifestation of the Radiants' power. However, if I recall correctly, Shallan's mother says something to the effect of "she's one of them" and tries to kill her because of her manifestations of power (pattern, shardblade). So I think it's fair to say that the mother isn't an envisager.

I think it's the second one, but not quite for that reason. I think we can agree that Nightblood and shardblades are similar-ish in creation. Unless I'm misremembering, when Shardblades cut through things, they cause a slight fog/mist. Nightblood, because it's more invested, just vaporizes everything. But when in contact, it makes sense to me that you'd be able to duel as if both were Shards or both were just steel. That's my take anyway, and it seems like a logical path Brandon would take. I don't think he would bring over Nightblood just for it to instantly trump shardblades, which are amazing in their own right.