Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Phyresis

Enchant creature
Enchanted creature has infect. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Arcane Signet

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

Golgari Signet

Phyrexian Plaguelord

{T}, Sacrifice Phyrexian Plaguelord: Target creature gets -4/-4 until end of turn.
Sacrifice a creature: Target creature gets -1/-1 until end of turn.

Basilica Screecher

Flying
Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)

Plague of Vermin

Starting with you, each player may pay any amount of life. Repeat this process until no one pays life. Each player creates a 1/1 black Rat creature token for each 1 life they paid this way.

Spreading Plague

Whenever a creature enters the battlefield, destroy all other creatures that share a color with it. They can't be regenerated.

Plague Spitter

At the beginning of your upkeep, Plague Spitter deals 1 damage to each creature and each player.
When Plague Spitter dies, it deals 1 damage to each creature and each player.

Plague Fiend

Whenever Plague Fiend deals combat damage to a creature, destroy that creature unless its controller pays {2}.

Plague Stinger

Flying
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Dirge Bat

Mutate {4}{B}{B} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Flash
Flying
Whenever this creature mutates, destroy target creature or planeswalker an opponent controls.

Isolation Zone

When Isolation Zone enters the battlefield, exile target creature or enchantment an opponent controls until Isolation Zone leaves the battlefield. (That permanent returns under its owner's control.)

Strength of Isolation

Enchant creature
Enchanted creature gets +1/+2 and has protection from black.
Madness {W} (If you discard this card, discard it into exile. When you do, cast it for its madness cost or put it into your graveyard.)

Isolated Chapel

Isolated Chapel enters the battlefield tapped unless you control a Plains or a Swamp.
{T}: Add {W} or {B}.

Dakmor Plague

Dakmor Plague deals 3 damage to each creature and each player.

Fungal Infection

Target creature gets -1/-1 until end of turn. Create a 1/1 green Saproling creature token.

Necrotic Plague

Enchant creature
Enchanted creature has "At the beginning of your upkeep, sacrifice this creature."
When enchanted creature dies, its controller chooses target creature one of their opponents controls. Return Necrotic Plague from its owner's graveyard to the battlefield attached to that creature.

Karona, False God

Haste
At the beginning of each player's upkeep, that player untaps Karona, False God and gains control of it.
Whenever Karona attacks, creatures of the creature type of your choice get +3/+3 until end of turn.

Orzhov Signet

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Plague Mare

Plague Mare can't be blocked by white creatures.
When Plague Mare enters the battlefield, creatures your opponents control get -1/-1 until end of turn.

Plague Wind

Destroy all creatures you don't control. They can't be regenerated.

Infectious Host

When Infectious Host dies, target player loses 2 life.

Plague Wight

Whenever Plague Wight becomes blocked, each creature blocking it gets -1/-1 until end of turn.

Plague Beetle

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)

Instill Infection

Put a -1/-1 counter on target creature.
Draw a card.

Isolated Watchtower

{T}: Add {C}.
{2}, {T}: Scry 1, then you may reveal the top card of your library. If a basic land card is revealed this way, put it onto the battlefield tapped. Activate only if an opponent controls at least two more lands than you.

Plague Engineer

Deathtouch
As Plague Engineer enters the battlefield, choose a creature type.
Creatures of the chosen type your opponents control get -1/-1.

Sick and Tired

Two target creatures each get -1/-1 until end of turn.

Quarantine Field

Quarantine Field enters the battlefield with X isolation counters on it.
When Quarantine Field enters the battlefield, for each isolation counter on it, exile up to one target nonland permanent an opponent controls until Quarantine Field leaves the battlefield.

Triumph of the Hordes

Until end of turn, creatures you control get +1/+1 and gain trample and infect. (Creatures with infect deal damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Infected Vermin

{2}{B}: Infected Vermin deals 1 damage to each creature and each player.
Threshold — {3}{B}: Infected Vermin deals 3 damage to each creature and each player. Activate only if seven or more cards are in your graveyard.

Blighted Bat

Flying
{1}: Blighted Bat gains haste until end of turn.

Plague Boiler

At the beginning of your upkeep, put a plague counter on Plague Boiler.
{1}{B}{G}: Put a plague counter on Plague Boiler or remove a plague counter from it.
When Plague Boiler has three or more plague counters on it, sacrifice it. If you do, destroy all nonland permanents.

Undercity Plague

Target player loses 1 life, discards a card, then sacrifices a permanent.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

Phyrexian Arena

At the beginning of your upkeep, you draw a card and you lose 1 life.

Kelsien, the Plague

Vigilance, haste
Kelsien, the Plague gets +1/+1 for each experience counter you have.
{T}: Kelsien deals 1 damage to target creature you don't control. When that creature dies this turn, you get an experience counter.

Sol Ring

Isolation Cell

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

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Homeward Path

{T}: Add {C}.
{T}: Each player gains control of all creatures they own.

Infectious Horror

Whenever Infectious Horror attacks, each opponent loses 2 life.

Sickening Shoal

You may exile a black card with mana value X from your hand rather than pay this spell's mana cost.
Target creature gets -X/-X until end of turn.

Traveling Plague

Enchant creature
At the beginning of each upkeep, put a plague counter on Traveling Plague.
Enchanted creature gets -1/-1 for each plague counter on Traveling Plague.
When enchanted creature leaves the battlefield, that creature's controller returns Traveling Plague from its owner's graveyard to the battlefield.

Krovikan Plague

Enchant non-Wall creature you control
When Krovikan Plague enters the battlefield, draw a card at the beginning of the next turn's upkeep.
Tap enchanted creature: Krovikan Plague deals 1 damage to any target. Put a -0/-1 counter on enchanted creature. Activate only if enchanted creature is untapped.

Eternal Isolation

Put target creature with power 4 or greater on the bottom of its owner's library.

Endemic Plague

As an additional cost to cast this spell, sacrifice a creature.
Destroy all creatures that share a creature type with the sacrificed creature. They can't be regenerated.

Tainted Strike

Target creature gets +1/+0 and gains infect until end of turn. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Plague Witch

{B}, {T}, Discard a card: Target creature gets -1/-1 until end of turn.

Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.

Plagued Rusalka

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

Virulent Plague

Mana Crypt

At the beginning of your upkeep, flip a coin. If you lose the flip, Mana Crypt deals 3 damage to you.
{T}: Add {C}{C}.

Garza Zol, Plague Queen

Flying, haste
Whenever a creature dealt damage by Garza Zol, Plague Queen this turn dies, put a +1/+1 counter on Garza Zol.
Whenever Garza Zol deals combat damage to a player, you may draw a card.

Engineered Plague

As Engineered Plague enters the battlefield, choose a creature type.
All creatures of the chosen type get -1/-1.

Spread the Sickness

Destroy target creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Grafted Exoskeleton

Equipped creature gets +2/+2 and has infect. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
Whenever Grafted Exoskeleton becomes unattached from a permanent, sacrifice that permanent.
Equip {2}

Isolate

Exile target permanent with mana value 1.

Temporal Isolation

Flash
Enchant creature
Enchanted creature has shadow. (It can block or be blocked by only creatures with shadow.)
Prevent all damage that would be dealt by enchanted creature.

Each player loses a third of their life, then discards a third of the cards in their hand, then sacrifices a third of the creatures they control, then sacrifices a third of the lands they control. Round up each time.

Gurmag Swiftwing

Smallpox

Each player loses 1 life, discards a card, sacrifices a creature, then sacrifices a land.

Plague Myr

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{T}: Add {C}.

Smothering Tithe

Whenever an opponent draws a card, that player may pay {2}. If the player doesn't, you create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")