Vorel of the Hull Clade!
Basically, ALL THE COUNTERS. Then use Vorel to double them, untap him, and keep doing it.
Overrun with a gazillion creatures
This is fantastic. I've been waiting for a deck like this. I can just imagine saying, "Why can't I hold all of these counters?"
Oh, stuff with persist + Master Biomancer gets silly :-)
What about Prime Speaker Zegana , for some card advantage + large creature.
I play this as my commander. You have helped me find graft creatures that I can use, and I wanted to mention a few of my game breakers: Phantom Nantuko , Phantom Centaur , Phantom Tiger , Spike Feeder , and Spike Weaver . The phantom creatures are nearly unkillable on their own. Adding Vorel just makes them crazy. The two spikes I play have crazy abilities that Vorel makes better (near unlimited life gain/fog).
Oh, you also made me realize you can duplicate the level up counters. I'm thinking of using Lighthouse Chronologist now. That would be funny in multi EDH.