Ajani's Pridemate

Whenever you gain life, put a +1/+1 counter on this creature.

Ajani, Strength of the Pride

+1: You gain life equal to the number of creatures you control plus the number of planeswalkers you control.
−2: Create a 2/2 white Cat Soldier creature token named Ajani's Pridemate with "Whenever you gain life, put a +1/+1 counter on Ajani's Pridemate."
0: If you have at least 15 life more than your starting life total, exile Ajani, Strength of the Pride and each artifact and creature your opponents control.

Grimclimb Pathway

Brightclimb Pathway

Brightclimb Pathway // Grimclimb Pathway

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.)

Bloodthirsty Aerialist

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

Radiant Fountain

When Radiant Fountain enters, you gain 2 life.
{T}: Add {C}.

Heliod, Sun-Crowned

Indestructible
As long as your devotion to white is less than five, Heliod isn't a creature.
Whenever you gain life, put a +1/+1 counter on target creature or enchantment you control.
{1}{W}: Another target creature gains lifelink until end of turn.

Plains

Scion of the Swarm

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

Healer's Hawk

Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Light of Promise

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

Godless Shrine

({T}: Add {W} or {B}.)
As Godless Shrine enters, you may pay 2 life. If you don't, it enters tapped.

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.

Isolated Chapel

Isolated Chapel enters tapped unless you control a Plains or a Swamp.
{T}: Add {W} or {B}.