These were introduced at last Duskruin. Here are the relevant wiki links about them... https://gswiki.play.net/NightShroudCloak https://gswiki.play.net/NightShroudcloak/saved_posts
This is an off the shelf version and is not unlocked. You have to be at least 1x trained in stalk/hide for some of the scripts to work. Depending on the unlock level, the cloak has chances to autohide you when you are attacked.
These sold for 7,500 bloodscrip for the off the shelf version.
A mithglin-buttoned billowing black greatcloak - cb: 10 mil buyout Roblar
Weighs 6, holds 140. Max light and deep.