Wicked Reflection

Whenever a creature enters the battlefield under
your opponent's control, you may pay {x}, where
X is it's converted mana cost. If you do, create a
token that's a copy of that creature, except it's a
black Nightmare and has "This creature can only
block creatures with the same name as it." and
"This creature cannot attack unless a creature
with the same name as it attacked last turn."
A perfect reflection in every way, except it's eyes.
Those were much too dark.