Kambal, Consul of Allocation

Whenever an opponent casts a noncreature spell, that player loses 2 life and you gain 2 life.

Sanguine Bond

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

Soul Warden

Whenever another creature enters, you gain 1 life.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Liesa, Shroud of Dusk

Rather than pay {2} for each previous time you've cast this spell from the command zone this game, pay 2 life that many times.
Flying, lifelink
Whenever a player casts a spell, they lose 2 life.

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.

Liesa, Forgotten Archangel

Flying, lifelink
Whenever another nontoken creature you control dies, return that card to its owner's hand at the beginning of the next end step.
If a creature an opponent controls would die, exile it instead.

Suture Priest

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