Claws of Gix

{1}, Sacrifice a permanent: You gain 1 life.

Hallow

Prevent all damage target spell would deal this turn. You gain life equal to the damage prevented this way.

Ajani's Pridemate

Whenever you gain life, put a +1/+1 counter on Ajani's Pridemate.

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.

Nykthos Paragon

Whenever you gain life, you may put that many +1/+1 counters on each creature you control. Do this only once each turn.

Case of the Uneaten Feast

Whenever a creature enters the battlefield under your control, you gain 1 life.
To solve — You've gained 5 or more life this turn. (If unsolved, solve at the beginning of your end step.)
Solved — Sacrifice this Case: Creature cards in your graveyard gain "You may cast this card from your graveyard" until end of turn.

Radiant Fountain

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

Kabira Crossroads

Kabira Crossroads enters the battlefield tapped.
When Kabira Crossroads enters the battlefield, you gain 2 life.
{T}: Add {W}.

Scroll of Avacyn

{1}, Sacrifice Scroll of Avacyn: Draw a card. If you control an Angel, you gain 5 life.

Soul Warden

Whenever another creature enters the battlefield, you gain 1 life.

Revitalize

Ajani's Welcome

Whenever a creature enters the battlefield under your control, you gain 1 life.

Blossoming Calm

You gain hexproof until your next turn. You gain 2 life.
Rebound (If you cast this spell from your hand, exile it as it resolves. At the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.)

Ajani, Wise Counselor

+2: You gain 1 life for each creature you control.
−3: Creatures you control get +2/+2 until end of turn.
−9: Put X +1/+1 counters on target creature, where X is your life total.