Night of the Living Dead

Enchantment
When ~this~ comes into play, non-Zombie creatures get -2/-2 until end of turn.
At the end of each turn, each player puts a 2/2 Zombie token into play for each non-Zombie creature put into his or her graveyard from play this turn.
All Zombies have deathtouch.
It's the Magic equivalent of a zombie movie. First it kills off a bunch of the living, creating an undead horde. If a creature gets bitten, it dies and turns into a zombie.
Hum for

you get a weenie WOG and deathtouch zombies for everyone.
If you're playing a weenie army (which you shouldn't with this in your deck at 6cc) you'll turn them all into 2/2 eot zombies or they will gain deathtouch if they are already zombies.
Your opponent loses only 2 toughness or less creatures and also gets deathtouch zombies with which to attack you the next turn, in addition to the creatures with greater than 2 toughness that will take one of your zombies out of the game (as they probably have at least 2 power too) and give him a 2/2 deathtouch into the deal. Sweet for your opponent.
There's a few things I'd look at with this card:
If you want to create a zombie army, kill everything. Make them zombies. Chomp brain. Don't just cull the weak, WoG them and deal with the rest. (Granted, mass kill is not really a zombie effect flavourwise but you are assured zombies on the board)
"When ~this~ comes into play, destroy all non-Zombie creatures."
If you prefer to stay with the -2/-2 idea, make it static. A static -2/-2 for non-zombies is nice on a

card.
"Non-Zombie creatures have -2/-2."
The only other thing I'd suggest flavourwise is this: (though it's going in a different direction)
In zombie movies, when a guy gets munched by the zombies he goes to the other side, he becomes a zombie against the hero team. You could incorporate this and avoid recursion trickery (because NotLD would be pretty insane with Nether Traitors, enough

and a sac outlet, say Claws of Gix). Why not go the following route:
"When a non-zombie creature is put into a graveyard from play, put it into play under target opponent's control. It is Black and is a Brain Munching Zombie.
All Zombies have deathtouch."
Fun card but at 6cc something you want to benefit yourself more than your opponent.