I got lucky with the Arc Blade challenge and got it on the first Vanguard strike. Got the Undying Mind strike where you go backwards through the garden. I'm on Xbone, so it was the first time I've seen this strike. I completed the whole challenge in the boss room. They dump a LOT of Major Precursor Vex on you. Made it really easy, comparatively. The Voidwalker challenge is idiotic without cheesing it, which I intend to do. Nova Bombs into large groups only net 2 or 3 orbs. It's BS. Edit: The 3 Hive in the basement aren't working for me. Only get 6 orbs.