Woodcaller Automaton - 292 R BRO

Prototype {2}{G}{G} — 3/3 (You may cast this spell with different mana cost, color, and size. It keeps its abilities and types.)
When this creature enters, if you cast it, untap target land you control. It becomes a Treefolk creature with haste and base power and toughness equal to this creature's power and toughness. It's still a land.

rare
Artifact Creature — Construct
From the Magic: The Gathering set The Brothers' War.