Kaervek the Merciless

Whenever an opponent casts a spell, Kaervek the Merciless deals damage equal to that spell's mana value to any target.

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.)

Polluted Bonds

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

Underworld Dreams

Whenever an opponent draws a card, Underworld Dreams deals 1 damage to that player.

Ob Nixilis, Unshackled

Flying, trample
Whenever an opponent searches their library, that player sacrifices a creature and loses 10 life.
Whenever another creature dies, put a +1/+1 counter on Ob Nixilis, Unshackled.

Kaervek's Spite

As an additional cost to cast this spell, sacrifice all permanents you control and discard your hand.
Target player loses 5 life.

Kaervek's Hex

Kaervek's Hex deals 1 damage to each nonblack creature and an additional 1 damage to each green creature.

Kaervek's Purge

Destroy target creature with mana value X. If that creature dies this way, Kaervek's Purge deals damage equal to the creature's power to the creature's controller.

Zo-Zu the Punisher

Whenever a land enters, Zo-Zu the Punisher deals 2 damage to that land's controller.

Price of Glory

Whenever a player taps a land for mana, if it's not that player's turn, destroy that land.

Harsh Mentor

Whenever an opponent activates an ability of an artifact, creature, or land on the battlefield, if it isn't a mana ability, Harsh Mentor deals 2 damage to that player.

Isolation Cell

Whenever an opponent casts a creature spell, that player loses 2 life unless they pay {2}.

Kaervek's Torch

As long as Kaervek's Torch is on the stack, spells that target it cost {2} more to cast.
Kaervek's Torch deals X damage to any target.

Painful Quandary

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

Manabarbs

Whenever a player taps a land for mana, Manabarbs deals 1 damage to that player.