Soul Warden

Whenever another creature enters, you gain 1 life.

Marauding Blight-Priest

Whenever you gain life, each opponent loses 1 life.

Swamp

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.

Vampire's Kiss

Target player loses 2 life and you gain 2 life. Create two Blood tokens. (They're artifacts with "{1}, {T}, Discard a card, Sacrifice this artifact: Draw a card.")

Sign in Blood

Target player draws two cards and loses 2 life.

Celestial Unicorn

Whenever you gain life, put a +1/+1 counter on Celestial Unicorn.

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Vampire Spawn

When this creature enters, each opponent loses 2 life and you gain 2 life.

Obscura Storefront

When Obscura Storefront enters, sacrifice it. When you do, search your library for a basic Plains, Island, or Swamp card, put it onto the battlefield tapped, then shuffle and you gain 1 life.