Bloodthirsty Conqueror

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

Dina, Soul Steeper

Whenever you gain life, each opponent loses 1 life.
{1}, Sacrifice another creature: Dina gets +X/+0 until end of turn, where X is the sacrificed creature's power.

Forest

Cauldron Familiar

When this creature enters, each opponent loses 1 life and you gain 1 life.
Sacrifice a Food: Return this card from your graveyard to the battlefield.

Exquisite Blood

Whenever an opponent loses life, you gain that much life.

Mindcrank

Whenever an opponent loses life, that player mills that many cards. (Damage causes loss of life.)