Debt to the Deathless

Each opponent loses two times X life. You gain life equal to the life lost this way.

Blood Tithe

Each opponent loses 3 life. You gain life equal to the life lost this way.

Subversion

At the beginning of your upkeep, each opponent loses 1 life. You gain life equal to the life lost this way.

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Exquisite Blood

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

Crypt Ghast

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.)
Whenever you tap a Swamp for mana, add an additional {B}.

Rhox Faithmender

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
If you would gain life, you gain twice that much life instead.

Kaya, Orzhov Usurper

+1: Exile up to two target cards from a single graveyard. You gain 2 life if at least one creature card was exiled this way.
−1: Exile target nonland permanent with mana value 1 or less.
−5: Kaya deals damage to target player equal to the number of cards that player owns in exile and you gain that much life.

Indulging Patrician

Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)
At the beginning of your end step, if you gained 3 or more life this turn, each opponent loses 3 life.

Angel of Vitality

Flying
If you would gain life, you gain that much life plus 1 instead.
This creature gets +2/+2 as long as you have 25 or more life.

Blood Tribute

Kicker—Tap an untapped Vampire you control. (You may tap a Vampire you control in addition to any other costs as you cast this spell.)
Target opponent loses half their life, rounded up. If this spell was kicked, you gain life equal to the life lost this way.

Scholar of Athreos

{2}{B}: Each opponent loses 1 life. You gain life equal to the life lost this way.

Angel of Destiny

Flying, double strike
Whenever a creature you control deals combat damage to a player, you and that player each gain that much life.
At the beginning of your end step, if you have at least 15 life more than your starting life total, each player this creature attacked this turn loses the game.

Spirit Loop

Enchant creature you control
Whenever enchanted creature deals damage, you gain that much life.
When this Aura is put into a graveyard from the battlefield, return it to its owner's hand.

Licia, Sanguine Tribune

This spell costs {1} less to cast for each 1 life you gained this turn.
First strike, lifelink
Pay 5 life: Put three +1/+1 counters on Licia. Activate only during your turn and only once each turn.

Archangel of Thune

Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Whenever you gain life, put a +1/+1 counter on each creature you control.

Chancellor of the Dross

You may reveal this card from your opening hand. If you do, at the beginning of the first upkeep, each opponent loses 3 life, then you gain life equal to the life lost this way.
Flying, lifelink

Serra Ascendant

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
As long as you have 30 or more life, this creature gets +5/+5 and has flying.

Souls of the Faultless

Defender (This creature can't attack.)
Whenever this creature is dealt combat damage, you gain that much life and attacking player loses that much life.

Vampiric Link

Enchant creature
Whenever enchanted creature deals damage, you gain that much life.

Tormented Hero

This creature enters tapped.
Heroic — Whenever you cast a spell that targets this creature, each opponent loses 1 life. You gain life equal to the life lost this way.

Beacon of Immortality

Double target player's life total. Shuffle Beacon of Immortality into its owner's library.

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.)

Malakir Bloodwitch

Flying, protection from white
When this creature enters, each opponent loses life equal to the number of Vampires you control. You gain life equal to the life lost this way.

Gray Merchant of Asphodel

When this creature enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)