Rotwood Mulcher

{t}, Sacrifice a land: Add {b} or {g}.
Whenever a land is put into your graveyard from
the battlefield, you may search your library for a
Basic Forest card and put it into your hand, then
shuffle.
Threshold -- Exile three lands from your
graveyard: Add {b} or {g}. Activate this ability only
as a sorcery, and only if seven or more cards are
in your graveyard.