The Bindings, drop on any difficulty or heroic/mythic only?
It should be any difficulty.
And do you have to kill the bosses in question with the Dreadblades equipped, or is it enough for them to be in your inventory?
They just need to be in your bag. Drop rate sucks, so it will take a lot of runs.
Good, just got the left binding off Dagrul, now to spam Vault of the Wardens.
Um, also got the right half from my second run of Vaults. What else do I need now?
Looks like I need to do Stormheim’s quest line.
EDIT: Yup, needed to progress through the Stormheim campaign to talk to the Dragon I needed, and now I got my Hidden Artifact.
I got mine on the 1st and 2nd kill