Curse of the Undead

Whenever a Zombie you control dies, put two
copies of it onto the battlefield.
Whenever a player casts a Zombie spell, put a 2/2
black Zombie creature token onto the battlefield.
Whenever a Zombie you control becomes the
target of a spell an opponent controls, you may sacrifice this Zombie.
If you do, this player loses life equal to the
mana costs of this spell.