Fumulus, the Infestation

Flying, deathtouch
Whenever a player sacrifices a nontoken creature, create a 1/1 black Insect creature token with flying.
Whenever an Insect, Leech, Slug, or Worm you control attacks, defending player loses 1 life and you gain 1 life.

Vein Ripper

Flying
Ward—Sacrifice a creature.
Whenever a creature dies, target opponent loses 2 life and you gain 2 life.

Scion of the Swarm

Flying
Whenever you gain life, put a +1/+1 counter on this creature.

Eternal Thirst

Enchant creature
Enchanted creature has lifelink and "Whenever a creature an opponent controls dies, put a +1/+1 counter on this creature." (Damage dealt by a creature with lifelink also causes its controller to gain that much life.)

Exquisite Blood

Whenever an opponent loses life, you gain that much life.

Bloodcrazed Socialite

Menace
When this creature enters, create a Blood token. (It's an artifact with "{1}, {T}, Discard a card, Sacrifice this token: Draw a card.")
Whenever this creature attacks, you may sacrifice a Blood token. If you do, it gets +2/+2 until end of turn.

Swarm of Bloodflies

Flying
This creature enters with two +1/+1 counters on it.
Whenever another creature dies, put a +1/+1 counter on this creature.

Consumed by Greed

Gift a card (You may promise an opponent a gift as you cast this spell. If you do, they draw a card before its other effects.)
Target opponent sacrifices a creature with the greatest power among creatures they control. If the gift was promised, return target creature card from your graveyard to your hand.

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 of their choice, then sacrifices a third of the lands they control of their choice. Round up each time.

Bloodthirsty Blade

Equipped creature gets +2/+0 and is goaded. (It attacks each combat if able and attacks a player other than you if able.)
{1}: Attach this Equipment to target creature an opponent controls. Activate only as a sorcery.

Blood Pact

Target player draws two cards and loses 2 life.

Parting Thoughts

Destroy target creature. You draw X cards and you lose X life, where X is the number of counters on that creature.

Mole Worms

You may choose not to untap this creature during your untap step.
{T}: Tap target land. It doesn't untap during its controller's untap step for as long as this creature remains tapped.

Invoke Despair

Target opponent sacrifices a creature of their choice. If they can't, they lose 2 life and you draw a card. Then repeat this process for an enchantment and a planeswalker.

Foul Renewal

Return target creature card from your graveyard to your hand. Target creature gets -X/-X until end of turn, where X is the toughness of the card returned this way.

Swarmyard Massacre

Create two 1/1 green Squirrel creature tokens. Then each creature that isn't an Insect, Rat, Spider, or Squirrel gets -1/-1 until end of turn for each creature you control that's an Insect, Rat, Spider, or Squirrel.

Archon of Cruelty

Flying
Whenever this creature enters or attacks, target opponent sacrifices a creature or planeswalker of their choice, discards a card, and loses 3 life. You draw a card and gain 3 life.

Endless Cockroaches

When this creature dies, return it to its owner's hand.

Pestilent Syphoner

Flying
Toxic 1 (Players dealt combat damage by this creature also get a poison counter.)

Glistening Sphere

This artifact enters tapped.
When this artifact enters, proliferate.
{T}: Add one mana of any color.
Corrupted — {T}: Add three mana of any one color. Activate only if an opponent has three or more poison counters.

Bitterblossom

At the beginning of your upkeep, you lose 1 life and create a 1/1 black Faerie Rogue creature token with flying.

Falkenrath Forebear

Flying
This creature can't block.
Whenever this creature deals combat damage to a player, create a Blood token.
{B}, Sacrifice two Blood tokens: Return this card from your graveyard to the battlefield.

Skithiryx, the Blight Dragon

Flying
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
{B}: Skithiryx gains haste until end of turn.
{B}{B}: Regenerate Skithiryx.

Smallpox

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

Plaguecrafter

When this creature enters, each player sacrifices a creature or planeswalker of their choice. Each player who can't discards a card.

Lurking Skirge

When a creature is put into an opponent's graveyard from the battlefield, if this permanent is an enchantment, it becomes a 3/2 Phyrexian Imp creature with flying.

Huskburster Swarm

This spell costs {1} less to cast for each creature card you own in exile and in your graveyard.
Menace, deathtouch

Bankrupt in Blood

As an additional cost to cast this spell, sacrifice two creatures.
Draw three cards.

Rank and File

When this creature enters, green creatures get -1/-1 until end of turn.

Mirkwood Bats

Flying
Whenever you create or sacrifice a token, each opponent loses 1 life.

Thief of Blood

Flying
As this creature enters, remove all counters from all permanents. This creature enters with a +1/+1 counter on it for each counter removed this way.

Zof Bloodbog

Zof Consumption

Each opponent loses 4 life and you gain 4 life.

Zof Consumption // Zof Bloodbog

Blasphemous Edict

You may pay {B} rather than pay this spell's mana cost if there are thirteen or more creatures on the battlefield.
Each player sacrifices thirteen creatures of their choice.

Mortarpod

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +0/+1 and has "Sacrifice this creature: This creature deals 1 damage to any target."
Equip {2}

Infestation Sage

When this creature dies, create a 1/1 black and green Insect creature token with flying.

Dismember

({B/P} can be paid with either {B} or 2 life.)
Target creature gets -5/-5 until end of turn.

Inkmoth Nexus

{T}: Add {C}.
{1}: This land becomes a 1/1 Phyrexian Blinkmoth artifact creature with flying and infect until end of turn. It's still a land. (It deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)

Barter in Blood

Each player sacrifices two creatures of their choice.

Malicious Invader

Flying
This creature gets +2/+0 as long as an opponent controls a Human.

Innocent Traveler

At the beginning of your upkeep, any opponent may sacrifice a creature of their choice. If no one does, transform this creature.

Innocent Traveler // Malicious Invader

Feed the Swarm

Destroy target creature or enchantment an opponent controls. You lose life equal to that permanent's mana value.

Marsh Casualties

Kicker {3} (You may pay an additional {3} as you cast this spell.)
Creatures target player controls get -1/-1 until end of turn. If this spell was kicked, those creatures get -2/-2 until end of turn instead.

Wall of Blood

Defender (This creature can't attack.)
Pay 1 life: This creature gets +1/+1 until end of turn.

Necrosquito

Flying
This creature enters with two oil counters on it.
This creature gets +1/+1 for each oil counter on it.
Whenever another creature or artifact you control is put into a graveyard from the battlefield, put an oil counter on this creature.

Eumidian Hatchery

{T}, Pay 1 life: Add {B}. Put a hatchling counter on this land.
When this land is put into a graveyard from the battlefield, for each hatchling counter on it, create a 1/1 black Insect creature token with flying.

No Mercy

Whenever a creature deals damage to you, destroy it.

Imp's Mischief

Change the target of target spell with a single target. You lose life equal to that spell's mana value.

Heartstabber Mosquito

Kicker {2}{B} (You may pay an additional {2}{B} as you cast this spell.)
Flying
When this creature enters, if it was kicked, destroy target creature.

Bloodline Bidding

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Choose a creature type. Return all creature cards of the chosen type from your graveyard to the battlefield.

Giant Fly

Flying
Whenever you sacrifice another permanent, this creature gets +1/+0 until end of turn.

Swamp

Abyssal Gatekeeper

When this creature dies, each player sacrifices a creature of their choice.

Sheoldred's Edict

Choose one —
• Each opponent sacrifices a nontoken creature of their choice.
• Each opponent sacrifices a creature token of their choice.
• Each opponent sacrifices a planeswalker of their choice.

Infest

All creatures get -2/-2 until end of turn.

Swarmyard

{T}: Add {C}.
{T}: Regenerate target Insect, Rat, Spider, or Squirrel. (The next time it would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Innocent Blood

Each player sacrifices a creature of their choice.

Dystopia

Cumulative upkeep—Pay 1 life. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
At the beginning of each player's upkeep, that player sacrifices a green or white permanent of their choice.

Swamp Mosquito

Flying
Whenever this creature attacks and isn't blocked, defending player gets a poison counter. (A player with ten or more poison counters loses the game.)

Sick and Tired

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

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 this card from its owner's graveyard to the battlefield attached to that creature.

Bonepicker Skirge

Flying
Corrupted — As long as an opponent has three or more poison counters, this creature has deathtouch and lifelink.

Phyrexian Vatmother

Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.)
At the beginning of your upkeep, you get a poison counter.

The Seedcore

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast Phyrexian creature spells.
Corrupted — {T}: Target 1/1 creature gets +2/+1 until end of turn. Activate only if an opponent has three or more poison counters.

Sign in Blood

Hideous End

Destroy target nonblack creature. Its controller loses 2 life.

Exsanguinate

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

Swat

Destroy target creature with power 2 or less.
Cycling {2} ({2}, Discard this card: Draw a card.)