Creature — Elemental Horror 3/6, 3BBG (6)
Rare
{1}{B}{G}, {T}: Target Forest becomes a 4/4 black and green Elemental Horror creature. It's still a land.
"Its darkened sap penetrates natural fibers and spreads its own genes. Emulation experiments are underway."
—Simic research notes
Illus. Greg Staples

10/1/2005: The effect has no stated duration, so a land turned into a creature this way continues being a creature as long as the land is on the battlefield.
8/1/2008: A noncreature permanent that turns into a creature is subject to the "summoning sickness" rule: It can only attack, and its {T} abilities can only be activated, if its controller has continuously controlled that permanent since the beginning of his or her most recent turn.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern