Finally! 5/5 Shadow Hunter, what an absolute pain in the arse good grief, based on my experience farming it, what I've seen posted here and heard in conversations with people I'm very confident its a 1% drop chance. Drop rate appears to be the same across all difficulties and there is no evidence to support it being higher on master, if anyone have anything to report here feel free to share it.

Here's a breakdown of my own experience:
Shoes I obtained within 50 runs without realizing it farming while goblin for friendslop points, this is easily one of the easiest pieces to farm.
Top I obtained after around 220 runs, easy piece but rng was really bad for me.
Shorts I obtained around 60 runs in, this was the slowest instance to traverse.
Gloves are by far the easiest drop, got them in around 30 runs, you can just H and be semi-afk for this farm.
Mask is BY FAR the worst, ihatecrossbowssomuch holy moly, clocked in at around 60 runs.

Going to go for the weapon soon. Oh and a bonus observation, bane lord seems to spawn in about 1 in 50 on average.