A friend of mine told me last night that they could not get Dark Shade to work for them, no matter what they did, so I said I'd test it out and record it, if not.
https://youtu.be/YkObcdLsuMQ Here, you can see that it heads over towards the minotaur I'm attacking and just stands there. This was casting it before I attacked the minotaur, as that was how I previously used the skill.
After some deliberation with another player in discord, they asked if I needed to be close up to the minotaur and so I gave that a shot:
https://youtu.be/BLskl-vqdPs and same result.
PC NA server, though I'm not sure if it matters...