Altar of the Everlasting World

When Altar of the Everlasting World enters the battlefield, search your library for a basic land card
and place it on the battlefield tapped. If that land
is a Forest, put a World counter on this
enchantment.
{1}: Add {g} to your mana pool for each World
counter on Altar of the Everlasting World.
{4}{g}{g}{g}: Creatures you control get +4/+4 and trample.