OK, I will try and find a better one (I had one where all the Nether Tentacles were lined up in a row), but basically anytime you run into a Unique pack of mobs that have Missile Dampening as one of their affixes, and you're on your Demon Hunter, you should start giggling and clapping your hands excitedly like a little child.
So for those unaware, missile dampening (that blue circle in the picture above) slows down any missiles that enter the area. So you fire an arrow, it hits the blue shield, it slows down to a crawl. When I first saw this, I thought I was screwed.
But if you fire Nether Tentacles at it, you know what happens? The Tentacles stop moving, and slow inch forward. All you need to do is watch as the mob runs towards you and gets hit, repeatedly, by the NT as it procs over and over and over and over again. It's like a little black hole of death.
If everyone knew this already and I am late to the party, I apologize. I will try and grab a video of it when I can, but I just thought I would share it now. It's not often an affix of a monster works against them so badly in conjunction with a Demon Hunter, so it's nice to grab the upper hand once in a while.
If you see missile dampening, give it a try, and watch as the mobs explode into tiny pieces rather quickly.
Update: Boom, several people on YouTube already posted a video!