Swarm Supremacy

Undergrowth - When Swarm Supremacy enters
the battlefield, return creature cards with total
converted mana cost X from your graveyard to
the battlefield, where X is the number of
creature cards in your graveyard.
Whenever a black or green permanent that you
own leaves the battlefield, you may pay {b/g}. If
you do, distribute X +1/+1 counters to up to X
target creatures you control, where X is that black
or green permanent's converted mana cost.