Gonti's Machinations

Whenever you lose life for the first time each turn, you get {E}. (You get an energy counter. Damage causes loss of life.)
Pay {E}{E}, Sacrifice this enchantment: Each opponent loses 3 life. You gain life equal to the life lost this way.

Oath of Lim-Dûl

Whenever you lose life, for each 1 life you lost, sacrifice a permanent other than this enchantment unless you discard a card. (Damage dealt to you causes you to lose life.)
{B}{B}: Draw a card.

No Mercy

Whenever a creature deals damage to you, destroy it.

Exquisite Blood

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

Triskaidekaphobia

At the beginning of your upkeep, choose one —
• Each player with exactly 13 life loses the game, then each player gains 1 life.
• Each player with exactly 13 life loses the game, then each player loses 1 life.

Vilis, Broker of Blood

Flying
{B}, Pay 2 life: Target creature gets -1/-1 until end of turn.
Whenever you lose life, draw that many cards. (Damage causes loss of life.)

Koskun Falls

At the beginning of your upkeep, sacrifice this enchantment unless you tap an untapped creature you control.
Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Shauku, Endbringer

Flying
Shauku can't attack if there's another creature on the battlefield.
At the beginning of your upkeep, you lose 3 life.
{T}: Exile target creature and put a +1/+1 counter on Shauku.

Sower of Discord

Flying
As this creature enters, choose two players.
Whenever damage is dealt to one of the chosen players, the other chosen player also loses that much life.

Tree of Perdition

Defender
{T}: Exchange target opponent's life total with this creature's toughness.