Creature — Vampire Shaman 1/1, 1B (2)
Common
Whenever a creature enters the battlefield under an opponent's control, you may have that player lose 1 life.
A drop now is all he needs to find you later.
Illus. Greg Staples

9/22/2011: Life loss is not the same as damage. Blood Seeker's ability will not cause creatures with bloodthirst to enter the battlefield with +1/+1 counters.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern