Ditto

When Ditto enters the battlefield, you may
choose target creature. Ditto becomes a copy of
that creature until that creature leaves the battlefield.
At the beginning of your upkeep, if Ditto is not a
copy of a creature, you may choose target
creature. Ditto becomes a copy of that creature
until that creature leaves the battlefield.
Capable of copying an enemy's genetic code to
instantly transform itself into a duplicate of
the enemy.