http://www.wizards.com/Magic/Magazine/Article.aspx?x=mtg/daily/arcana/1152

The Simic Combine is always evolving—literally! The evolve mechanic means your creatures are constantly growing into new and unusual forms. A creature with evolve gets a +1/+1 counter if a larger creature (meaning it has a greater power or a greater toughness) enters the battlefield under your control. After enough evolutions, even the smallest creature can sit on top of the food chain.

The "Simic Synthesis" deck takes full advantage of creatures with high power and low toughness, or vice versa. Crocanura and Adaptive Snapjaw grow large quickly because most other creatures in the deck can cause them to evolve. Before you know it, you'll be rolling over your opponent with gigantic creatures.

One of the key spells in this deck is Bioshift. For only Green or Blue Mana, you can take all of the +1/+1 counters from a single creature and move them elsewhere. Not only can you suddenly make a creature larger in the middle of combat, but you can also use Bioshift to regress one of your evolved creature back to its original state so it can evolve all over again! In conjunction with Sapphire Drake and Crowned Ceratok, Bioshift can also give a creature flying or trample out of nowhere.

If you're looking to kick up the +1/+1 counter theme another notch, take a look at Primordial Hydra from the Magic 2013 core set. This huge Hydra doubles the number of +1/+1 counters on it every turn, giving you plenty of fuel for Bioshift. And don't miss the undying mechanic from the Dark Ascension and Avacyn Restored sets. When these creatures die, they come back with a +1/+1 counter—an upgrade to itself and potentially your creatures with evolve!