Blood Seeker

Whenever a creature an opponent controls enters, you may have that player lose 1 life.

Bloodthirsty Conqueror

Flying, deathtouch
Whenever an opponent loses life, you gain that much life. (Damage causes loss of life.)

Bloodlord of Vaasgoth

Bloodthirst 3 (If an opponent was dealt damage this turn, this creature enters with three +1/+1 counters on it.)
Flying
Whenever you cast a Vampire creature spell, it gains bloodthirst 3.

Exsanguinator Cavalry

Menace, lifelink
Whenever a Knight you control deals combat damage to a player, put a +1/+1 counter on that creature and create a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this token: Draw a card.")