Manabarbs

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

Citadel of Pain

At the beginning of each player's end step, Citadel of Pain deals X damage to that player, where X is the number of untapped lands they control.

Impatience

At the beginning of each player's end step, if that player didn't cast a spell this turn, Impatience deals 2 damage to that player.

Kaervek the Merciless

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

Storm World

At the beginning of each player's upkeep, Storm World deals X damage to that player, where X is 4 minus the number of cards in their hand.

Lavaborn Muse

At the beginning of each opponent's upkeep, if that player has two or fewer cards in hand, Lavaborn Muse deals 3 damage to that player.

Tevesh Szat, Doom of Fools

+2: Create two 0/1 black Thrull creature tokens.
+1: You may sacrifice another creature or planeswalker. If you do, draw two cards, then draw another card if the sacrificed permanent was a commander.
−10: Gain control of all commanders. Put all commanders from the command zone onto the battlefield under your control.
Tevesh Szat, Doom of Fools can be your commander.
Partner

Kediss, Emberclaw Familiar

Whenever a commander you control deals combat damage to an opponent, it deals that much damage to each other opponent.
Partner (You can have two commanders if both have partner.)

Price of Knowledge

Players have no maximum hand size.
At the beginning of each opponent's upkeep, Price of Knowledge deals damage to that player equal to the number of cards in that player's hand.

Paupers' Cage

At the beginning of each opponent's upkeep, if that player has two or fewer cards in hand, Paupers' Cage deals 2 damage to that player.

Pyrohemia

At the beginning of the end step, if no creatures are on the battlefield, sacrifice Pyrohemia.
{R}: Pyrohemia deals 1 damage to each creature and each player.

Kederekt Parasite

Whenever an opponent draws a card, if you control a red permanent, you may have Kederekt Parasite deal 1 damage to that player.

Lim-Dûl's Hex

At the beginning of your upkeep, for each player, Lim-Dûl's Hex deals 1 damage to that player unless they pay {B} or {3}.

Pestilence

At the beginning of the end step, if no creatures are on the battlefield, sacrifice Pestilence.
{B}: Pestilence deals 1 damage to each creature and each player.

Desolation

At the beginning of each end step, each player who tapped a land for mana this turn sacrifices a land of their choice. Desolation deals 2 damage to each player who sacrificed a Plains this way.

Iron Maiden

At the beginning of each opponent's upkeep, Iron Maiden deals X damage to that player, where X is the number of cards in their hand minus 4.

Rivalry

At the beginning of each player's upkeep, if that player controls more lands than each other player, Rivalry deals 2 damage to them.

Court of Ire

When Court of Ire enters, you become the monarch.
At the beginning of your upkeep, Court of Ire deals 2 damage to any target. If you're the monarch, it deals 7 damage instead.

Spiteful Visions

At the beginning of each player's draw step, that player draws an additional card.
Whenever a player draws a card, Spiteful Visions deals 1 damage to that player.

Rackling

At the beginning of each opponent's upkeep, Rackling deals X damage to that player, where X is 3 minus the number of cards in their hand.

Power Surge

At the beginning of each player's upkeep, Power Surge deals X damage to that player, where X is the number of untapped lands they controlled at the beginning of this turn.

War's Toll

Whenever an opponent taps a land for mana, tap all lands that player controls.
If a creature an opponent controls attacks, all creatures that opponent controls attack if able.

Stoneshaker Shaman

At the beginning of each player's end step, that player sacrifices an untapped land of their choice.

Skullcage

At the beginning of each opponent's upkeep, Skullcage deals 2 damage to that player unless they have exactly three or exactly four cards in hand.