Artifact Creature - Shapeshifter X/7-X, 6 (6) As Shapeshifter comes into play, choose a number between 0 and 7. At the beginning of your upkeep, you may choose a number between 0 and 7. Shapeshifter's power is equal to the last chosen number and its toughness is equal to 7 minus that number.1 Born like a Phoenix from the Flame, But neither Bulk nor Shape the same. -Jonathan Swift, "Vanbrug's House"
Illus. Dan Frazier
The power/toughness change is a triggered ability that occurs only once each upkeep. [D'Angelo 2000/02/25]
The change affects the initial power/toughness, not the current power/toughness. [D'Angelo 1998/06/05]
If it begins upkeep with power of 2 or less, the Dwarven Warriors may be tapped to make it unblockable before you change the Shapeshifter to be a 6/1 creature. [Aahz 1994/06/01]
Note - This card had no creature type until Oracle 2007/10/01, when it became "Shapeshifter".