Xantcha, Sleeper Agent

Flying

Your opponents can't gain life.

At the beginning of each end step, each opponent loses life equal to the life that player lost this turn. (Damage causes loss of life.)

Astral Cornucopia enters the battlefield with X charge counters on it.

{T}: Choose a color. Add one mana of that color for each charge counter on Astral Cornucopia.

Banefire deals X damage to any target.

If X is 5 or more, this spell can't be countered and the damage can't be prevented.

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)

Target creature gets -X/-X until end of turn. You gain X life.

Put X -1/-1 counters on each creature. Shuffle Black Sun's Zenith into its owner's library.

Blaze deals X damage to any target.

Flying

At the beginning of your upkeep, target player draws a card and loses 1 life.

{T}: Add {B} or {R}.

As an additional cost to cast this spell, pay X life.

Each other player loses X life.

Bonfire of the Damned deals X damage to target player or planeswalker and each creature that player or that planeswalker's controller controls.

Miracle {X}{R} (You may cast this card for its miracle cost when you draw it if it's the first card you drew this turn.)

Destroy X target artifacts. Builder's Bane deals damage to each player equal to the number of artifacts they controlled that were put into a graveyard this way.

Burn from Within deals X damage to any target. If a creature is dealt damage this way, it loses indestructible until end of turn. If that creature would die this turn, exile it instead.

Destroy X target artifacts.

Charcoal Diamond enters the battlefield tapped.

{T}: Add {B}.

Chimeric Mass enters the battlefield with X charge counters on it.

{1}: Until end of turn, Chimeric Mass becomes a Construct artifact creature with "This creature's power and toughness are each equal to the number of charge counters on it."

Multikicker {1} (You may pay an additional {1} any number of times as you cast this spell.)

Choose any target, then choose another target for each time this spell was kicked. Comet Storm deals X damage to each of them.

{T}: Add one mana of any color in your commander's color identity.

Sacrifice Commander's Sphere: Draw a card.

Crater's Claws deals X damage to any target.

Ferocious — Crater's Claws deals X plus 2 damage instead if you control a creature with power 4 or greater.

Cut deals 4 damage to target creature.

Flying, trample

When Demonlord Belzenlok enters the battlefield, exile cards from the top of your library until you exile a nonland card, then put that card into your hand. If the card's mana value is 4 or greater, repeat this process. Demonlord Belzenlok deals 1 damage to you for each card put into your hand this way.

Search your library for up to X cards, put those cards into your hand, then shuffle.

Search your library for a card, put that card into your hand, then shuffle.

{T}: Add {C}{C}{C}.

{3}, {T}, Sacrifice Dreamstone Hedron: Draw three cards.

Destroy X target nonblack creatures. Draw X cards.

Multikicker {2} (You may pay an additional {2} any number of times as you cast this spell.)

Everflowing Chalice enters the battlefield with a charge counter on it for each time it was kicked.

{T}: Add {C} for each charge counter on Everflowing Chalice.

Each opponent loses X life. You gain life equal to the life lost this way.

Fire Diamond enters the battlefield tapped.

{T}: Add {R}.

{T}: Add three mana of any one color.

Guardian Idol enters the battlefield tapped.

{T}: Add {C}.

{2}: Guardian Idol becomes a 2/2 Golem artifact creature until end of turn.

{T}: Add {C}{C}.

{2}, {T}, Sacrifice Hedron Archive: Draw two cards.

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)

Flying

At the beginning of your end step, each opponent discards a card.

{1}{B}, Sacrifice an artifact: Target creature gets -2/-2 until end of turn.

Flying

At the beginning of your upkeep, draw a card unless target opponent sacrifices a creature or pays 3 life.

{T}: Add {R}.

When Khalni Gem enters the battlefield, return two lands you control to their owner's hand.

{T}: Add two mana of any one color.

{T}: Add {B} or {R}.

{4}{B}{R}: Kolaghan Monument becomes a 4/4 black and red Dragon artifact creature with flying until end of turn.

Flying

Whenever a permanent owned by another player is put into a graveyard from the battlefield, you draw a card and you lose 1 life.

{T}: Add {B}.

When Liliana's Contract enters the battlefield, you draw four cards and you lose 4 life.

At the beginning of your upkeep, if you control four or more Demons with different names, you win the game.

Maga, Traitor to Mortals enters the battlefield with X +1/+1 counters on it.

When Maga enters the battlefield, target player loses life equal to the number of +1/+1 counters on it.

Choose one —

• Search your library for a card, put it into your hand, then shuffle.

• Put a card you own from outside the game into your hand.

Target player discards X cards at random.

({T}: Add {R}.)

You draw two cards and you lose 2 life.

Landfall — Whenever a land enters the battlefield under your control, you may have target player lose 3 life. If you do, put three +1/+1 counters on Ob Nixilis, the Fallen.

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.

{T}: Add {C}{C}.

Choose two —

• Target player loses X life.

• Return target creature card with mana value X or less from your graveyard to the battlefield.

• Target creature gets -X/-X until end of turn.

• Up to X target creatures gain fear until end of turn. (They can't be blocked except by artifact creatures and/or black creatures.)

{T}: Add {B} or {R}.

{B}{R}, {T}, Sacrifice Rakdos Cluestone: Draw a card.

{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.

Rakdos's Return deals X damage to target opponent or planeswalker. That player or that planeswalker's controller discards X cards.

Red Sun's Zenith deals X damage to any target. If a creature dealt damage this way would die this turn, exile it instead. Shuffle Red Sun's Zenith into its owner's library.

Flying

When Rune-Scarred Demon enters the battlefield, search your library for a card, put it into your hand, then shuffle.

{T}: Add {C}{C}.

{T}: Add {C}{C}.

Return target creature card with mana value X or less from your graveyard to the battlefield.

({T}: Add {B}.)

{T}: Add {C}{C}{C}.

Repeat the following process X times. Each opponent loses 3 life unless that player sacrifices a nonland permanent or discards a card.

{T}: Add {C}{C}.

You may pay {1} and return a basic land you control to its owner's hand rather than pay this spell's mana cost.

Veinfire Borderpost enters the battlefield tapped.

{T}: Add {B} or {R}.

Worn Powerstone enters the battlefield tapped.

{T}: Add {C}{C}.