Bomb Squad

{T}: Put a fuse counter on target creature.
At the beginning of your upkeep, put a fuse counter on each creature with a fuse counter on it.
Whenever a creature has four or more fuse counters on it, remove all fuse counters from it and destroy it. That creature deals 4 damage to its controller.

Archfiend of Ifnir

Flying
Whenever you cycle or discard another card, put a -1/-1 counter on each creature your opponents control.
Cycling {2} ({2}, Discard this card: Draw a card.)

Blast Zone

Blast Zone enters with a charge counter on it.
{T}: Add {C}.
{X}{X}, {T}: Put X charge counters on Blast Zone.
{3}, {T}, Sacrifice Blast Zone: Destroy each nonland permanent with mana value equal to the number of charge counters on Blast Zone.

Eye of Doom

When Eye of Doom enters, each player chooses a nonland permanent and puts a doom counter on it.
{2}, {T}, Sacrifice Eye of Doom: Destroy each permanent with a doom counter on it.

Arcane Spyglass

{2}, {T}, Sacrifice a land: Draw a card and put a charge counter on Arcane Spyglass.
Remove three charge counters from Arcane Spyglass: Draw a card.

Athreos, Shroud-Veiled

Indestructible
As long as your devotion to white and black is less than seven, Athreos isn't a creature.
At the beginning of your end step, put a coin counter on another target creature.
Whenever a creature with a coin counter on it dies or is put into exile, return that card to the battlefield under your control.

Assemble the Legion

At the beginning of your upkeep, put a muster counter on Assemble the Legion. Then create a 1/1 red and white Soldier creature token with haste for each muster counter on Assemble the Legion.

Beastmaster Ascension

Whenever a creature you control attacks, you may put a quest counter on Beastmaster Ascension.
As long as Beastmaster Ascension has seven or more quest counters on it, creatures you control get +5/+5.

Gibbering Descent

At the beginning of each player's upkeep, that player loses 1 life and discards a card.
Hellbent — Skip your upkeep step if you have no cards in hand.
Madness {2}{B}{B} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Azor's Elocutors

At the beginning of your upkeep, put a filibuster counter on Azor's Elocutors. Then if Azor's Elocutors has five or more filibuster counters on it, you win the game.
Whenever a source deals damage to you, remove a filibuster counter from Azor's Elocutors.

As Foretold

At the beginning of your upkeep, put a time counter on As Foretold.
Once each turn, you may pay {0} rather than pay the mana cost for a spell you cast with mana value X or less, where X is the number of time counters on As Foretold.

Black Mana Battery

{2}, {T}: Put a charge counter on Black Mana Battery.
{T}, Remove any number of charge counters from Black Mana Battery: Add {B}, then add an additional {B} for each charge counter removed this way.

Armageddon Clock

At the beginning of your upkeep, put a doom counter on Armageddon Clock.
At the beginning of your draw step, Armageddon Clock deals damage equal to the number of doom counters on it to each player.
{4}: Remove a doom counter from Armageddon Clock. Any player may activate this ability but only during any upkeep step.

Descent into Avernus

At the beginning of your upkeep, put two descent counters on Descent into Avernus. Then each player creates X Treasure tokens and Descent into Avernus deals X damage to each player, where X is the number of descent counters on Descent into Avernus.

Infinite Hourglass

At the beginning of your upkeep, put a time counter on Infinite Hourglass.
All creatures get +1/+0 for each time counter on Infinite Hourglass.
{3}: Remove a time counter from Infinite Hourglass. Any player may activate this ability but only during any upkeep step.

Barrin's Codex

At the beginning of your upkeep, you may put a page counter on Barrin's Codex.
{4}, {T}, Sacrifice Barrin's Codex: Draw X cards, where X is the number of page counters on Barrin's Codex.

Archery Training

Enchant creature
At the beginning of your upkeep, you may put an arrow counter on Archery Training.
Enchanted creature has "{T}: This creature deals X damage to target attacking or blocking creature, where X is the number of arrow counters on Archery Training."

Tobias, Doomed Conqueror

Flash
When Tobias, Doomed Conqueror dies, for each nontoken creature you controlled that died this turn, create a 2/2 black Zombie creature token.

Doom Foretold

At the beginning of each player's upkeep, that player sacrifices a nonland, nontoken permanent of their choice. If that player can't, they discard a card, they lose 2 life, you draw a card, you gain 2 life, you create a 2/2 white Knight creature token with vigilance, then you sacrifice Doom Foretold.

Powder Keg

At the beginning of your upkeep, you may put a fuse counter on Powder Keg.
{T}, Sacrifice Powder Keg: Destroy each artifact and creature with mana value equal to the number of fuse counters on Powder Keg.

Infused Arrows

Sunburst (This enters with a charge counter on it for each color of mana spent to cast it.)
{T}, Remove X charge counters from Infused Arrows: Target creature gets -X/-X until end of turn.

Black Market

Whenever a creature dies, put a charge counter on Black Market.
At the beginning of your first main phase, add {B} for each charge counter on Black Market.

Lavabrink Floodgates

{T}: Add {R}{R}.
At the beginning of each player's upkeep, that player may put a doom counter on Lavabrink Floodgates or remove a doom counter from it. Then if it has three or more doom counters on it, sacrifice Lavabrink Floodgates. When you do, it deals 6 damage to each creature.

Kardur, Doomscourge

When Kardur, Doomscourge enters, until your next turn, creatures your opponents control attack each combat if able and attack a player other than you if able.
Whenever an attacking creature dies, each opponent loses 1 life and you gain 1 life.

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

Altar of Shadows

At the beginning of your first main phase, add {B} for each charge counter on Altar of Shadows.
{7}, {T}: Destroy target creature. Then put a charge counter on Altar of Shadows.

Imminent Doom

Imminent Doom enters with a doom counter on it.
Whenever you cast a spell with mana value equal to the number of doom counters on Imminent Doom, Imminent Doom deals that much damage to any target. Then put a doom counter on Imminent Doom.

Crackling Doom

Crackling Doom deals 2 damage to each opponent. Each opponent sacrifices a creature with the greatest power among creatures that player controls.

Archmage Ascension

At the beginning of each end step, if you drew two or more cards this turn, you may put a quest counter on Archmage Ascension.
As long as Archmage Ascension has six or more quest counters on it, if you would draw a card, you may instead search your library for a card, put that card into your hand, then shuffle.

Descent into Madness

At the beginning of your upkeep, put a despair counter on Descent into Madness, then each player exiles X permanents they control and/or cards from their hand, where X is the number of despair counters on Descent into Madness.

Incendiary

Enchant creature
At the beginning of your upkeep, you may put a fuse counter on Incendiary.
When enchanted creature dies, Incendiary deals X damage to any target, where X is the number of fuse counters on Incendiary.

Time Bomb

At the beginning of your upkeep, put a time counter on Time Bomb.
{1}, {T}, Sacrifice Time Bomb: Time Bomb deals damage equal to the number of time counters on it to each creature and each player.

Aria of Flame

When Aria of Flame enters, each opponent gains 10 life.
Whenever you cast an instant or sorcery spell, put a verse counter on Aria of Flame, then it deals damage equal to the number of verse counters on it to target player or planeswalker.

Alaundo the Seer

{T}: Draw a card, then exile a card from your hand and put a number of time counters on it equal to its mana value. It gains "When the last time counter is removed from this card, if it's exiled, you may cast it without paying its mana cost. If you cast a creature spell this way, it gains haste until end of turn." Then remove a time counter from each other card you own in exile.

Scuttling Doom Engine

Scuttling Doom Engine can't be blocked by creatures with power 2 or less.
When Scuttling Doom Engine dies, it deals 6 damage to target opponent or planeswalker.

Cyclone

At the beginning of your upkeep, put a wind counter on Cyclone, then sacrifice Cyclone unless you pay {G} for each wind counter on it. If you pay, Cyclone deals damage equal to the number of wind counters on it to each creature and each player.

Goblin Bomb

At the beginning of your upkeep, you may flip a coin. If you win the flip, put a fuse counter on Goblin Bomb. If you lose the flip, remove a fuse counter from Goblin Bomb.
Remove five fuse counters from Goblin Bomb and sacrifice it: It deals 20 damage to target player or planeswalker.