Death's Shadow

Death's Shadow gets -X/-X, where X is your life total.

Bhaal, Lord of Murder

As long as your life total is less than or equal to half your starting life total, Bhaal, Lord of Murder has indestructible.
Whenever another nontoken creature you control dies, put a +1/+1 counter on target creature and goad it.

Rite of Consumption

As an additional cost to cast this spell, sacrifice a creature.
Rite of Consumption deals damage equal to the sacrificed creature's power to target player or planeswalker. You gain life equal to the damage dealt this way.

Necropotence

Skip your draw step.
Whenever you discard a card, exile that card from your graveyard.
Pay 1 life: Exile the top card of your library face down. Put that card into your hand at the beginning of your next end step.

Moltensteel Dragon

({R/P} can be paid with either {R} or 2 life.)
Flying
{R/P}: Moltensteel Dragon gets +1/+0 until end of turn.

Pain's Reward

Each player may bid life. You start the bidding with a bid of any number. In turn order, each player may top the high bid. The bidding ends if the high bid stands. The high bidder loses life equal to the high bid and draws four cards.

Bane, Lord of Darkness

As long as your life total is less than or equal to half your starting life total, Bane, Lord of Darkness has indestructible.
Whenever another nontoken creature you control dies, target opponent may have you draw a card. If they don't, you may put a creature card with equal or lesser toughness from your hand onto the battlefield.

Greven, Predator Captain

Menace
Greven, Predator Captain gets +X/+0, where X is the amount of life you've lost this turn.
Whenever Greven attacks, you may sacrifice another creature. If you do, you draw cards equal to that creature's power and you lose life equal to that creature's toughness.

Ad Nauseam

Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value. You may repeat this process any number of times.

Ali from Cairo

Damage that would reduce your life total to less than 1 reduces it to 1 instead.

Fortune Thief

Damage that would reduce your life total to less than 1 reduces it to 1 instead.
Morph {R}{R} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Chainer's Torment

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I, II — Chainer's Torment deals 2 damage to each opponent and you gain 2 life.
III — Create an X/X black Nightmare Horror creature token, where X is half your life total, rounded up. It deals X damage to you.