Grollub

Whenever Grollub is dealt damage, each opponent gains that much life.

False Cure

Until end of turn, whenever a player gains life, that player loses 2 life for each 1 life they gained.

Reverse the Sands

Redistribute any number of players' life totals. (Each of those players gets one life total back.)

Have

Delighted Halfling

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a legendary spell, and that spell can't be countered.

Tree of Perdition

Defender
{T}: Exchange target opponent's life total with Tree of Perdition's toughness.

Wound Reflection

At the beginning of each end step, each opponent loses life equal to the life they lost this turn. (Damage causes loss of life.)

Aria of Flame

When Aria of Flame enters, each opponent gains 10 life.
Whenever you cast an instant or sorcery spell, put a verse counter on Aria of Flame, then it deals damage equal to the number of verse counters on it to target player or planeswalker.

Plague Drone

Flying
Rot Fly — If an opponent would gain life, that player loses that much life instead.

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.

Celestial Mantle

Enchant creature
Enchanted creature gets +3/+3.
Whenever enchanted creature deals combat damage to a player, double its controller's life total.

Greater Auramancy

Other enchantments you control have shroud. (A permanent with shroud can't be the target of spells or abilities.)
Enchanted creatures you control have shroud.

Kenrith, the Returned King

{R}: All creatures gain trample and haste until end of turn.
{1}{G}: Put a +1/+1 counter on target creature.
{2}{W}: Target player gains 5 life.
{3}{U}: Target player draws a card.
{4}{B}: Put target creature card from a graveyard onto the battlefield under its owner's control.

Rain of Gore

If a spell or ability would cause its controller to gain life, that player loses that much life instead.

Mithril Coat

Flash
Indestructible
When Mithril Coat enters, attach it to target legendary creature you control.
Equipped creature has indestructible.
Equip {3}

Tainted Remedy

If an opponent would gain life, that player loses that much life instead.

Isochron Scepter

Imprint — When Isochron Scepter enters, you may exile an instant card with mana value 2 or less from your hand.
{2}, {T}: You may copy the exiled card. If you do, you may cast the copy without paying its mana cost.

Hunters' Feast

Any number of target players each gain 6 life.

Beacon of Immortality

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

Alms Beast

Creatures blocking or blocked by Alms Beast have lifelink.

Wall of Shards

Defender, flying
Cumulative upkeep—An opponent gains 1 life. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)

Collapsing Borders

Domain — At the beginning of each player's upkeep, that player gains 1 life for each basic land type among lands they control. Then Collapsing Borders deals 3 damage to that player.

Vizkopa Guildmage

{1}{W}{B}: Target creature gains lifelink until end of turn.
{1}{W}{B}: Whenever you gain life this turn, each opponent loses that much life.

Kavu Predator

Trample
Whenever an opponent gains life, put that many +1/+1 counters on Kavu Predator.