G'rok Th'ar, Nature's Warden

{b/g}{b/g}, Put G'rok Th'ar into your graveyard from
your hand or the command zone: Reveal the top
six cards of your library. You may put any
number of creature cards from among them into
your graveyard. Put the rest on the bottom of
your library in a random order
When this creature enters the battlefield from
your graveyard, return all Troll creatures from
your graveyard to the battlefield under the
control of whoever controls G'rok Th'ar