Blood Researcher

Menace (This creature can't be blocked except by two or more creatures.)
Whenever you gain life, put a +1/+1 counter on Blood Researcher.

Vito, Thorn of the Dusk Rose

Whenever you gain life, target opponent loses that much life.
{3}{B}{B}: Creatures you control gain lifelink until end of turn.

Marauding Blight-Priest

Whenever you gain life, each opponent loses 1 life.

Starscape Cleric

Offspring {2}{B} (You may pay an additional {2}{B} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
Flying
This creature can't block.
Whenever you gain life, each opponent loses 1 life.

Enduring Tenacity

Whenever you gain life, target opponent loses that much life.
When Enduring Tenacity dies, if it was a creature, return it to the battlefield under its owner's control. It's an enchantment. (It's not a creature.)

Wall of Limbs

Defender (This creature can't attack.)
Whenever you gain life, put a +1/+1 counter on Wall of Limbs.
{5}{B}{B}, Sacrifice Wall of Limbs: Target player loses X life, where X is Wall of Limbs's power.

Bloodthirsty Aerialist

Flying
Whenever you gain life, put a +1/+1 counter on Bloodthirsty Aerialist.

Scion of the Swarm

Flying
Whenever you gain life, put a +1/+1 counter on Scion of the Swarm.

Bloodbond Vampire

Whenever you gain life, put a +1/+1 counter on Bloodbond Vampire.

Epicure of Blood

Sanguine Bond

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

Lisette, Dean of the Root

Whenever you gain life, you may pay {1}. If you do, put a +1/+1 counter on each creature you control and those creatures gain trample until end of turn.

Valentin, Dean of the Vein

Menace, lifelink
If a nontoken creature an opponent controls would die, exile it instead. When you do, you may pay {2}. If you do, create a 1/1 black and green Pest creature token with "When this creature dies, you gain 1 life."

Valentin, Dean of the Vein // Lisette, Dean of the Root

Vampire Scrivener

Flying
Whenever you gain life during your turn, put a +1/+1 counter on Vampire Scrivener.
Whenever you lose life during your turn, put a +1/+1 counter on Vampire Scrivener.

Trudge Garden

Whenever you gain life, you may pay {2}. If you do, create a 4/4 green Fungus Beast creature token with trample.

Veinwitch Coven

Menace
Whenever you gain life, you may pay {B}. If you do, return target creature card from your graveyard to your hand.

Defiant Bloodlord

Flying
Whenever you gain life, target opponent loses that much life.

Well of Lost Dreams

Whenever you gain life, you may pay {X}, where X is less than or equal to the amount of life you gained. If you do, draw X cards.

Dina, Soul Steeper

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