Ajani's Pridemate

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

Social Climber

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

Attended Healer

Whenever you gain life for the first time each turn, create a 1/1 white Cat creature token.
{2}{W}: Another target Cleric gains lifelink until end of turn.

Plains

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.

Accomplished Alchemist

{T}: Add one mana of any color.
{T}: Add X mana of any one color, where X is the amount of life you gained this turn.

Voice of the Blessed

Whenever you gain life, put a +1/+1 counter on Voice of the Blessed.
As long as Voice of the Blessed has four or more +1/+1 counters on it, it has flying and vigilance.
As long as Voice of the Blessed has ten or more +1/+1 counters on it, it has indestructible.

Trelasarra, Moon Dancer

Whenever you gain life, put a +1/+1 counter on Trelasarra, Moon Dancer and scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Blossoming Sands

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {G} or {W}.

Forest

Kor Celebrant

Whenever Kor Celebrant or another creature you control enters, you gain 1 life.

Sunbond

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