one single piece of gear is jusy too hard to choose, so I'd make an armor set called "Assassin's Shadow" it'd be the well preserved remains of an ancient assassin's gear from before the golden age. It'd be a battle torn black cloak. The chest piece would have a variety of daggers (all aesthetic) and poisons on it(poisons on a belt), with a sword on the back partially covered by the cloak. the helmet would actually be replaced by the assassin's mask(painted steel). A white mask with one eyehole as where the left eye would be, there is a burn mark. Where the mouth would be is the word "sleep" in Japanese. Makes some sense to be obtained from a Hive boss (you know, 'space zombies'). Advantages of this armor would be huge boost to stealth, large boost to melee (speed, damage, range, all or any). But disadvantages would be less defense than most legendary/exotic gear (from the gear being old) but not so much less that no one would use it. Obvious hunter gear.