Creature — Spirit Treefolk 3/3, 4G (5)
Uncommon
{2}{G}{G}: Yew Spirit gets +X/+X until end of turn, where X is its power.
"I wonder what dwelled in the primordial forests before humans existed."
—Elder Rimheit
Illus. Dan Scott

5/1/2012: The value of X is determined when the ability resolves. The bonus won't change later in the turn if the creature's power changes.
5/1/2012: If Yew Spirit has power less than 0, the "bonus" will be negative. For example, if it's somehow become -10/3, it would get -10/-10 and become -20/-7.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Standard (Type 2)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern