High Priority

Sproutback Trudge

This spell costs {X} less to cast, where X is the amount of life you gained this turn.
Trample
At the beginning of your end step, if you gained life this turn, you may cast Sproutback Trudge from your graveyard.

Dina, Soul Steeper

Whenever you gain life, each opponent loses 1 life.
{1}, Sacrifice another creature: Dina, Soul Steeper gets +X/+0 until end of turn, where X is the sacrificed creature's power.

Essence Depleter

Devoid (This card has no color.)
{1}{C}: Target opponent loses 1 life and you gain 1 life. ({C} represents colorless mana.)

Joyous Respite

You gain 1 life for each land you control.

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.

Roots of Life

As Roots of Life enters, choose Island or Swamp.
Whenever a land of the chosen type an opponent controls becomes tapped, you gain 1 life.

Tivash, Gloom Summoner

Lifelink
At the beginning of your end step, if you gained life this turn, you may pay X life, where X is the amount of life you gained this turn. If you do, create an X/X black Demon creature token with flying.

Fruition

You gain 1 life for each Forest on the battlefield.

Pontiff of Blight

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Other creatures you control have extort. (If a creature has multiple instances of extort, each triggers separately.)

Venser's Journal

You have no maximum hand size.
At the beginning of your upkeep, you gain 1 life for each card in your hand.

Respite

Prevent all combat damage that would be dealt this turn. You gain 1 life for each attacking creature.

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.

Return to Action

Until end of turn, target creature gets +1/+0 and gains lifelink and "When this creature dies, return it to the battlefield tapped under its owner's control."

Thoughtleech

Whenever an Island an opponent controls becomes tapped, you may gain 1 life.

Reaper's Talisman

Whenever equipped creature attacks, it gains deathtouch until end of turn.
Whenever equipped creature attacks alone, defending player loses 2 life and you gain 2 life.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Grazing Gladehart

Landfall — Whenever a land you control enters, you may gain 2 life.

Suffer the Past

Exile X target cards from target player's graveyard. For each card exiled this way, that player loses 1 life and you gain 1 life.

Blunt the Assault

You gain 1 life for each creature on the battlefield. Prevent all combat damage that would be dealt this turn.