Painful Quandary

Whenever an opponent casts a spell, that player loses 5 life unless they discard a card.

Irenicus's Vile Duplication

Create a token that's a copy of target creature you control, except the token has flying and it isn't legendary.

Sigil of Sleep

Enchant creature
Whenever enchanted creature deals damage to a player, return target creature that player controls to its owner's hand.

Helm of the Ghastlord

Enchant creature
As long as enchanted creature is blue, it gets +1/+1 and has "Whenever this creature deals damage to an opponent, draw a card."
As long as enchanted creature is black, it gets +1/+1 and has "Whenever this creature deals damage to an opponent, that player discards a card."

Polluted Bonds

Whenever a land an opponent controls enters, that player loses 2 life and you gain 2 life.

Y'shtola, Night's Blessed

Vigilance
At the beginning of each end step, if a player lost 4 or more life this turn, you draw a card.
Whenever you cast a noncreature spell with mana value 3 or greater, Y'shtola deals 2 damage to each opponent and you gain 2 life.

Monologue Tax

Whenever an opponent casts their second spell each turn, you create a Treasure token.

Revenge of Ravens

Whenever a creature attacks you or a planeswalker you control, that creature's controller loses 1 life and you gain 1 life.

Scrawling Crawler

At the beginning of your upkeep, each player draws a card.
Whenever an opponent draws a card, that player loses 1 life.

Ophidian Eye

Flash (You may cast this spell any time you could cast an instant.)
Enchant creature
Whenever enchanted creature deals damage to an opponent, you may draw a card.

Underworld Dreams

Whenever an opponent draws a card, this enchantment deals 1 damage to that player.

Vile Consumption

All creatures have "At the beginning of your upkeep, sacrifice this creature unless you pay 1 life."

Blind Obedience

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.)
Artifacts and creatures your opponents control enter tapped.

Sanguine Bond

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

Phyrexian Arena

At the beginning of your upkeep, you draw a card and you lose 1 life.

Sygg, River Cutthroat

At the beginning of each end step, if an opponent lost 3 or more life this turn, you may draw a card. (Damage causes loss of life.)

Liesa, Shroud of Dusk

Rather than pay {2} for each previous time you've cast this spell from the command zone this game, pay 2 life that many times.
Flying, lifelink
Whenever a player casts a spell, they lose 2 life.

Curiosity

Enchant creature
Whenever enchanted creature deals damage to an opponent, you may draw a card.

Bloodthirsty Conqueror

Flying, deathtouch
Whenever an opponent loses life, you gain that much life. (Damage causes loss of life.)

Kambal, Consul of Allocation

Whenever an opponent casts a noncreature spell, that player loses 2 life and you gain 2 life.

Sheoldred, the Apocalypse

Deathtouch
Whenever you draw a card, you gain 2 life.
Whenever an opponent draws a card, they lose 2 life.