Will, the Titan From Beneath

Will, the Titan from Beneath enters the
battlefield with burial counters on it equal to the number of cards in your library and becomes
buried. (It can't attack or block and has hexproof
as long as it's buried). When Will has no burial counters on it, it becomes unburied.
{4}: Remove burial counters from Will equal to
the number of creatures in your graveyard, then
if Will is unburied return all creature cards from
all graveyards to the battlefield under your
control.