Plunder the Graves from the Commander Anthology Box.
When black and green join forces, the graveyard is never the final resting place for a creature. If your opponents want to rid the board of your threats, exile is the only place that will truly keep them safe. Meren of Clan Nel Toth is a commander that specializes in ensuring that the more creatures that go to your graveyard, the fewer remain there. And with many potent sacrifice outlets, self-milling cards, and death triggers, you should have no worries about filling your graveyard with plenty of intimidating threats to recur. When you finally recur those threats and don't want to sacrifice them, you should have plenty of tokens to sacrifice in their stead thanks to ample token generation.