You can't win the game and your opponents can't lose the game.
6 /
6
{X}{B}{B}{B}
Agadeem's Awakening
Sorcery
Return from your graveyard to the battlefield any number of target creature cards that each have a different mana value X or less.
--
Agadeem, the Undercrypt
Land
As Agadeem, the Undercrypt enters the battlefield, you may pay 3 life. If you don't, it enters the battlefield tapped.
{T}: Add {B}.
{B}{B}{R}
Bedevil
Instant
Destroy target artifact, creature, or planeswalker.
--
Blackcleave Cliffs
Land
Blackcleave Cliffs enters the battlefield tapped unless you control two or fewer other lands.
{T}: Add {B} or {R}.
--
Blightstep Pathway
Land
{T}: Add {B}.
--
Searstep Pathway
Land
{T}: Add {R}.
--
Blood Crypt
Land - Swamp Mountain
({T}: Add {B} or {R}.)
As Blood Crypt enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.
--
Bloodstained Mire
Land
{T}, Pay 1 life, Sacrifice Bloodstained Mire: Search your library for a Swamp or Mountain card, put it onto the battlefield, then shuffle.
{B}{R}
Body Dropper
Creature - Devil Warrior
Whenever you sacrifice another creature, put a +1/+1 counter on Body Dropper.
{B}{R}, Sacrifice another creature: Body Dropper gains menace until end of turn. (It can't be blocked except by two or more creatures.)
2 /
2
{2}{R}
Brimstone Vandal
Creature - Devil
Menace (This creature can't be blocked except by two or more creatures.)
If it's neither day nor night, it becomes day as Brimstone Vandal enters the battlefield.
Whenever day becomes night or night becomes day, Brimstone Vandal deals 1 damage to each opponent.
2 /
3
--
Command Tower
Land
{T}: Add one mana of any color in your commander's color identity.
{2}{B}{B}
Demon of Catastrophes
Creature - Demon
As an additional cost to cast this spell, sacrifice a creature.
Flying, trample
6 /
6
{2}{R}
Devilish Valet
Creature - Devil Warrior
Trample, haste
Alliance -- Whenever another creature enters the battlefield under your control, double Devilish Valet's power until end of turn.
1 /
3
--
Dragonskull Summit
Land
Dragonskull Summit enters the battlefield tapped unless you control a Swamp or a Mountain.
{T}: Add {B} or {R}.
--
Fabled Passage
Land
{T}, Sacrifice Fabled Passage: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Then if you control four or more lands, untap that land.
{B}{R}
Fatal Grudge
Sorcery
As an additional cost to cast this spell, sacrifice a nonland permanent.
Each opponent chooses a permanent they control that shares a card type with the sacrificed permanent and sacrifices it.
Draw a card.
{B}
Fatal Push
Instant
Destroy target creature if it has mana value 2 or less.
Revolt -- Destroy that creature if it has mana value 4 or less instead if a permanent you controlled left the battlefield this turn.
{1}{R}
Festival Crasher
Creature - Devil
Whenever you cast an instant or sorcery spell, Festival Crasher gets +2/+0 until end of turn.
1 /
3
{4}{R}{R}
Fiendish Duo
Creature - Devil
First strike
If a source would deal damage to an opponent, it deals double that damage to that player instead.
5 /
5
{B/R}
Footlight Fiend
Creature - Devil
When Footlight Fiend dies, it deals 1 damage to any target.
1 /
1
{R}
Forge Devil
Creature - Devil
When Forge Devil enters the battlefield, it deals 1 damage to target creature and 1 damage to you.
1 /
1
--
Graven Cairns
Land
{T}: Add {C}.
{B/R}, {T}: Add {B}{B}, {B}{R}, or {R}{R}.
--
Haunted Ridge
Land
Haunted Ridge enters the battlefield tapped unless you control two or more other lands.
{T}: Add {B} or {R}.
{2}{R}{R}
Hellrider
Creature - Devil
Haste
Whenever a creature you control attacks, Hellrider deals 1 damage to the player or planeswalker it's attacking.
3 /
3
{3}{B}
Hidetsugu, Devouring Chaos
Legendary Creature - Ogre Demon
{B}, Sacrifice a creature: Scry 2.
{2}{R}, {T}: Exile the top card of your library. You may play that card this turn. When you exile a nonland card this way, Hidetsugu, Devouring Chaos deals damage equal to the exiled card's mana value to any target.
4 /
4
{1}{R}
Hobblefiend
Creature - Devil
Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
{1}, Sacrifice another creature: Put a +1/+1 counter on Hobblefiend.
2 /
1
--
Ifnir Deadlands
Land - Desert
{T}: Add {C}.
{T}, Pay 1 life: Add {B}.
{2}{B}{B}, {T}, Sacrifice a Desert: Put two -1/-1 counters on target creature an opponent controls. Activate only as a sorcery.
{2}{B}{R}
Kardur, Doomscourge
Legendary Creature - Demon Berserker
When Kardur, Doomscourge enters the battlefield, 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.
4 /
3
{1}{B}{R}
Kolaghan's Command
Instant
Choose two --
• Return target creature card from your graveyard to your hand.
• Target player discards a card.
• Destroy target artifact.
• Kolaghan's Command deals 2 damage to any target.
{R}
Lightning Bolt
Instant
Lightning Bolt deals 3 damage to any target.
{1}{B}{R}
Mahadi, Emporium Master
Legendary Creature - Cat Devil
At the beginning of your end step, create a Treasure token for each creature that died this turn. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
3 /
3
{3}{B}{R}
Master of Cruelties
Creature - Demon
First strike, deathtouch
Master of Cruelties can only attack alone.
Whenever Master of Cruelties attacks a player and isn't blocked, that player's life total becomes 1. Master of Cruelties assigns no combat damage this combat.
1 /
4
{1}{B}{R}
Mayhem Devil
Creature - Devil
Whenever a player sacrifices a permanent, Mayhem Devil deals 1 damage to any target.
3 /
3
{1}{R}
Mayhem Patrol
Creature - Devil Warrior
Menace (This creature can't be blocked except by two or more creatures.)
Whenever Mayhem Patrol attacks, target creature gets +1/+0 until end of turn.
Blitz {1}{R} (If you cast this spell for its blitz cost, it gains haste and "When this creature dies, draw a card." Sacrifice it at the beginning of the next end step.)
1 /
2
--
Mountain
Basic Land - Mountain
({T}: Add {R}.)
--
Mountain
Basic Land - Mountain
({T}: Add {R}.)
{2}{B}{B}
Nightmare Shepherd
Enchantment Creature - Demon
Flying
Whenever another nontoken creature you control dies, you may exile it. If you do, create a token that's a copy of that creature, except it's 1/1 and it's a Nightmare in addition to its other types.
4 /
4
{3}{B}{B}
Ob Nixilis of the Black Oath
Legendary Planeswalker - Nixilis
+2: Each opponent loses 1 life. You gain life equal to the life lost this way.
-2: Create a 5/5 black Demon creature token with flying. You lose 2 life.
-8: You get an emblem with "{1}{B}, Sacrifice a creature: You gain X life and draw X cards, where X is the sacrificed creature's power."
Ob Nixilis of the Black Oath can be your commander.
L:
3
--
Prismatic Vista
Land
{T}, Pay 1 life, Sacrifice Prismatic Vista: Search your library for a basic land card, put it onto the battlefield, then shuffle.
{B/R}
Rakdos Cackler
Creature - Devil
Unleash (You may have this creature enter the battlefield with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)
1 /
1
{B}{R}
Rakdos Headliner
Creature - Devil
Haste
Echo--Discard a card. (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
3 /
3
{3}
Rakdos Keyrune
Artifact
{T}: Add {B} or {R}.
{B}{R}: Rakdos Keyrune becomes a 3/1 black and red Devil artifact creature with first strike until end of turn.
{B}{B}{R}{R}
Rakdos, Lord of Riots
Legendary Creature - Demon
You can't cast this spell unless an opponent lost life this turn.
Flying, trample
Creature spells you cast cost {1} less to cast for each 1 life your opponents have lost this turn.
6 /
6
{4}{B}{R}
Rakdos, the Showstopper
Legendary Creature - Demon
Flying, trample
When Rakdos, the Showstopper enters the battlefield, flip a coin for each creature that isn't a Demon, Devil, or Imp. Destroy each creature whose coin comes up tails.
6 /
6
--
Ramunap Ruins
Land - Desert
{T}: Add {C}.
{T}, Pay 1 life: Add {R}.
{2}{R}{R}, {T}, Sacrifice a Desert: Ramunap Ruins deals 2 damage to each opponent.
{3}{B}{R}
Raphael, Fiendish Savior
Legendary Creature - Devil Noble
Flying
Other Demons, Devils, Imps, and Tieflings you control get +1/+1 and have lifelink.
At the beginning of each end step, if a creature card was put into your graveyard from anywhere this turn, create a 1/1 red Devil creature token with "When this creature dies, it deals 1 damage to any target."
4 /
4
{B}
Reanimate
Sorcery
Put target creature card from a graveyard onto the battlefield under your control. You lose life equal to its mana value.
{X}{R}{R}
Shatterskull Smashing
Sorcery
Shatterskull Smashing deals X damage divided as you choose among up to two target creatures and/or planeswalkers. If X is 6 or more, Shatterskull Smashing deals twice X damage divided as you choose among them instead.
--
Shatterskull, the Hammer Pass
Land
As Shatterskull, the Hammer Pass enters the battlefield, you may pay 3 life. If you don't, it enters the battlefield tapped.
{T}: Add {R}.
{2}{R}
Sin Prodder
Creature - Devil
Menace
At the beginning of your upkeep, reveal the top card of your library. Any opponent may have you put that card into your graveyard. If a player does, Sin Prodder deals damage to that player equal to that card's mana value. Otherwise, put that card into your hand.
3 /
2
--
Smoldering Marsh
Land - Swamp Mountain
({T}: Add {B} or {R}.)
Smoldering Marsh enters the battlefield tapped unless you control two or more basic lands.
{B}
Spark Harvest
Sorcery
As an additional cost to cast this spell, sacrifice a creature or pay {3}{B}.
Destroy target creature or planeswalker.
{2}{B}{B}
Spawn of Mayhem
Creature - Demon
Spectacle {1}{B}{B} (You may cast this spell for its spectacle cost rather than its mana cost if an opponent lost life this turn.)
Flying, trample
At the beginning of your upkeep, Spawn of Mayhem deals 1 damage to each player. Then if you have 10 or less life, put a +1/+1 counter on Spawn of Mayhem.
4 /
4
{2}{R}
Spiteful Prankster
Creature - Devil
As long as it's your turn, Spiteful Prankster has first strike.
Whenever another creature dies, Spiteful Prankster deals 1 damage to target player or planeswalker.
3 /
2
{1}{R}
Squealing Devil
Creature - Devil
Fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
When Squealing Devil enters the battlefield, you may pay {X}. If you do, target creature gets +X/+0 until end of turn.
When Squealing Devil enters the battlefield, sacrifice it unless {B} was spent to cast it.
2 /
1
--
Sulfurous Springs
Land
{T}: Add {C}.
{T}: Add {B} or {R}. Sulfurous Springs deals 1 damage to you.
--
Swamp
Basic Land - Swamp
({T}: Add {B}.)
--
Swamp
Basic Land - Swamp
({T}: Add {B}.)
{2}{B}
Taborax, Hope's Demise
Legendary Creature - Demon Cleric
Flying
Taborax, Hope's Demise has lifelink as long as it has five or more +1/+1 counters on it.
Whenever another nontoken creature you control dies, put a +1/+1 counter on Taborax. If that creature was a Cleric, you may draw a card. If you do, you lose 1 life.
2 /
2
{B}{R}
Terminate
Instant
Destroy target creature. It can't be regenerated.
{1}{R}
Tibalt's Rager
Creature - Devil
When Tibalt's Rager dies, it deals 1 damage to any target.
{1}{R}: Tibalt's Rager gets +2/+0 until end of turn.
1 /
2
{2}{R}
Tibalt, Rakish Instigator
Legendary Planeswalker - Tibalt
Your opponents can't gain life.
-2: Create a 1/1 red Devil creature token with "When this creature dies, it deals 1 damage to any target."
Return target creature card with mana value 3 or less from your graveyard to the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)
{2}{B}
Varragoth, Bloodsky Sire
Legendary Creature - Demon Rogue
Deathtouch
Boast -- {1}{B}: Target player searches their library for a card, then shuffles and puts that card on top. (Activate only if this creature attacked this turn and only once each turn.)
2 /
3
{1}{R}
Vengeful Devil
Creature - Devil
Haste
Morbid -- {T}: Vengeful Devil deals 1 damage to any target. Activate only if a creature died this turn.
1 /
1
{R}
Vexing Devil
Creature - Devil
When Vexing Devil enters the battlefield, any opponent may have it deal 4 damage to them. If a player does, sacrifice Vexing Devil.
4 /
3
{3}{R}
Wildfire Devils
Creature - Devil
When Wildfire Devils enters the battlefield and at the beginning of your upkeep, choose a player at random. That player exiles an instant or sorcery card from their graveyard. Copy that card. You may cast the copy without paying its mana cost.
4 /
2
{2}{R}
Witty Roastmaster
Creature - Devil Citizen
Alliance -- Whenever another creature enters the battlefield under your control, Witty Roastmaster deals 1 damage to each opponent.
3 /
2
{2}{R}{R}
Zariel, Archduke of Avernus
Legendary Planeswalker - Zariel
+1: Creatures you control get +1/+0 and gain haste until end of turn.
0: Create a 1/1 red Devil creature token with "When this creature dies, it deals 1 damage to any target."
-6: You get an emblem with "At the end of the first combat phase on your turn, untap target creature you control. After this phase, there is an additional combat phase."
L:
4
{2}{R}
Zurzoth, Chaos Rider
Legendary Creature - Devil
Whenever an opponent draws their first card each turn, if it's not their turn, you create a 1/1 red Devil creature token with "When this creature dies, it deals 1 damage to any target."
Whenever one or more Devils you control attack one or more players, you and those players each draw a card, then discard a card at random.
2 /
3
{1}{B}
Demonic Tutor
Sorcery
Search your library for a card, put that card into your hand, then shuffle.
{1}{B}{R}
Ob Nixilis, the Adversary
Legendary Planeswalker - Nixilis
Casualty X. The copy isn't legendary and has starting loyalty X. (As you cast this spell, you may sacrifice a creature with power X. When you do, copy this spell. The copy becomes a token.)
+1: Each opponent loses 2 life unless they discard a card. If you control a Demon or Devil, you gain 2 life.
-2: Create a 1/1 red Devil creature token with "When this creature dies, it deals 1 damage to any target."
-7: Target player draws seven cards and loses 7 life.