This deck is tied for my favorite to play that I currently own. The kill tactic is pretty self explanatory. Every creature serves a purpose. It's a little tight around 3CMC, as that's where most everything is. Though, with Korlash bringing in more Swamps and if Rooftop Storm happens to come around, it get's pretty ridiculous.
The Grim-Grin/Gravecrawler loop is pretty effective. Also, for the Unbreathing Horde; it is my understanding that tokens go into the graveyard then ceased to exist at the end of turn. I had a friend that tried cheating me out of some +1/+1 counters. Not to forget that it wouldn't matter due to combat phase rules as well.