The "Ability to Mark targets you damage" part of Keen Scout perk of the Nightstalker subclass doesn't work in crucible when you respawn with Felwinter's Artifact equipped.
However the Marking does work if you respawn and then equip Felwinter's Artifact.
-
Thank god no wall hacks [spoiler]just kidding[/spoiler] [spoiler]you hunters need all the help you can get[/spoiler] [spoiler]kappa[/spoiler]