Thirst for Blood

Enchant creature.
Gain control of enchanted creature.
at the beginning of each upkeep, if you
have less life than the enchanted creature's
owner, gain control of enchanted creature.
At the beginning of each end step if you have
more life than the enchanted creature's owner
then the creature's owner gains control of the
enchanted creature.
pay 2 life: draw a card then discard a card.