Syrane, Bloodvine Necromancer

You may play a land on each of your opponent's
turns. If you play a land on an opponent's turn,
it enters the battlefield under that opponent's
control.
Whenever an opponent taps a land you own for
mana, they add {1} more to what that land could
produce, then sacrifice it. You create a 1/1 black
and green Elf Zombie creature token.