Cleric of Life's Bond

Whenever another Cleric you control enters, you gain 1 life.
Whenever you gain life for the first time each turn, put a +1/+1 counter on Cleric of Life's Bond.

Scion of the Swarm

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

Marauding Blight-Priest

Whenever you gain life, each opponent loses 1 life.

Sun Droplet

Whenever you're dealt damage, put that many charge counters on Sun Droplet.
At the beginning of each upkeep, you may remove a charge counter from Sun Droplet. If you do, you gain 1 life.

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.

Bloodthirsty Aerialist

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

Light of Promise

Enchant creature
Enchanted creature has "Whenever you gain life, put that many +1/+1 counters on this creature."

Nyx-Fleece Ram

At the beginning of your upkeep, you gain 1 life.

Tend the Pests

As an additional cost to cast this spell, sacrifice a creature.
Create X 1/1 black and green Pest creature tokens with "When this creature dies, you gain 1 life," where X is the sacrificed creature's power.

Bloodbond Vampire

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

Celestial Unicorn

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

Fountain of Renewal

At the beginning of your upkeep, you gain 1 life.
{3}, Sacrifice Fountain of Renewal: Draw a card.

Sanguine Bond

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

Impassioned Orator

Whenever another creature you control enters, you gain 1 life.

Nightmare's Thirst

You gain 1 life. Target creature gets -X/-X until end of turn, where X is the amount of life you gained this turn.

Cleric Class

(Gain the next level as a sorcery to add its ability.)
If you would gain life, you gain that much life plus 1 instead.
{3}{W}: Level 2
Whenever you gain life, put a +1/+1 counter on target creature you control.
{4}{W}: Level 3
When this Class becomes level 3, return target creature card from your graveyard to the battlefield. You gain life equal to that creature's toughness.

Daxos, Blessed by the Sun

Daxos's toughness is equal to your devotion to white. (Each {W} in the mana costs of permanents you control counts toward your devotion to white.)
Whenever another creature you control enters or dies, you gain 1 life.

Soul Warden

Whenever another creature enters, you gain 1 life.

Twinblade Paladin

Whenever you gain life, put a +1/+1 counter on this creature.
As long as you have 25 or more life, this creature has double strike. (It deals both first-strike and regular combat damage.)