Fog of Gnats

Balemurk Leech

Eerie — Whenever an enchantment you control enters and whenever you fully unlock a Room, each opponent loses 1 life.

Infesting Radroach

Flying
Infesting Radroach can't block.
Whenever Infesting Radroach deals combat damage to a player, they get that many rad counters.
Whenever an opponent mills a nonland card, if Infesting Radroach is in your graveyard, you may return it to your hand.

Plague Fiend

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

Festerleech

Whenever Festerleech deals combat damage to a player, you mill two cards.
{1}{B}: Festerleech gets +2/+2 until end of turn. Activate only once each turn.

Mana Leech

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

Skittering Heartstopper

{B}: Skittering Heartstopper gains deathtouch until end of turn.

Stinging Cave Crawler

Deathtouch
Descend 4 — Whenever Stinging Cave Crawler attacks, if there are four or more permanent cards in your graveyard, you draw a card and you lose 1 life.

Bloatfly Swarm

Flying
Bloatfly Swarm enters with five +1/+1 counters on it.
If damage would be dealt to Bloatfly Swarm while it has a +1/+1 counter on it, prevent that damage, remove that many +1/+1 counters from it, then give each player a rad counter for each +1/+1 counter removed this way.

Slimy Dualleech

At the beginning of combat on your turn, target creature you control with power 2 or less gets +1/+0 and gains deathtouch until end of turn.

Death Charmer

Whenever Death Charmer deals combat damage to a creature, that creature's controller loses 2 life unless they pay {2}.

Brood of Cockroaches

When Brood of Cockroaches is put into your graveyard from the battlefield, at the beginning of the next end step, you lose 1 life and return Brood of Cockroaches to your hand.

Squelching Leeches

Squelching Leeches's power and toughness are each equal to the number of Swamps you control.

Blightbeetle

Protection from green (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything green.)
Creatures your opponents control can't have +1/+1 counters put on them.

Swamp Mosquito

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

Chainflail Centipede

Whenever Chainflail Centipede or equipped creature attacks, it gets +2/+0 until end of turn.
Reconfigure {2} ({2}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

Plague Beetle

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

Brain Maggot

When Brain Maggot enters, target opponent reveals their hand and you choose a nonland card from it. Exile that card until Brain Maggot leaves the battlefield.

Fretwork Colony

Fretwork Colony can't block.
At the beginning of your upkeep, put a +1/+1 counter on Fretwork Colony and you lose 1 life.

Wriggling Grub

When Wriggling Grub dies, create two 1/1 black and green Worm creature tokens.

Swarm of Bloodflies

Flying
Swarm of Bloodflies enters with two +1/+1 counters on it.
Whenever another creature dies, put a +1/+1 counter on Swarm of Bloodflies.

Stirge

Flying
Stirge can't block.
Blood Drain — {1}{B}, Pay 1 life, Sacrifice Stirge: Draw a card.

Necrosquito

Flying
Necrosquito enters with two oil counters on it.
Necrosquito 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 Necrosquito.

Virus Beetle

When Virus Beetle enters, each opponent discards a card.

Leeching Lurker

Lifelink
Nightbound (If a player casts at least two spells during their own turn, it becomes day next turn.)

Curse of Leeches

Enchant player
As this permanent transforms into Curse of Leeches, attach it to a player.
At the beginning of enchanted player's upkeep, they lose 1 life and you gain 1 life.
Daybound (If a player casts no spells during their own turn, it becomes night next turn.)

Curse of Leeches // Leeching Lurker

Pestilent Syphoner

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

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.)

Leech Gauntlet

Lifelink
Equipped creature has lifelink.
Reconfigure {4} ({4}: Attach to target creature you control; or unattach from a creature. Reconfigure only as a sorcery. While attached, this isn't a creature.)

Battlefly Swarm

Flying
{B}: Battlefly Swarm gains deathtouch until end of turn.

Mole Worms

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

Bilious Skulldweller

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

Phyrexian Battleflies

Flying
{B}: Phyrexian Battleflies gets +1/+0 until end of turn. Activate no more than twice each turn.

Blister Beetle

When Blister Beetle enters, target creature gets -1/-1 until end of turn.

Leechridden Swamp

({T}: Add {B}.)
Leechridden Swamp enters tapped.
{B}, {T}: Each opponent loses 1 life. Activate only if you control two or more black permanents.

Carrion Beetles

{2}{B}, {T}: Exile up to three target cards from a single graveyard.

Nantuko Shade

{B}: Nantuko Shade gets +1/+1 until end of turn.

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.

Endless Cockroaches

When Endless Cockroaches dies, return it to its owner's hand.

Mortician Beetle

Whenever a player sacrifices a creature, you may put a +1/+1 counter on Mortician Beetle.

Worms of the Earth

Players can't play lands.
Lands can't enter the battlefield.
At the beginning of each upkeep, any player may sacrifice two lands of their choice or have Worms of the Earth deal 5 damage to that player. If a player does either, destroy Worms of the Earth.

Insidious Bookworms

When Insidious Bookworms dies, you may pay {1}{B}. If you do, target player discards a card at random.

Rot Farm Mortipede

Whenever one or more creature cards leave your graveyard, Rot Farm Mortipede gets +1/+0 and gains menace and lifelink until end of turn.

Dune Beetle

Deadly Grub

Vanishing 3 (This creature enters with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
When Deadly Grub dies, if it had no time counters on it, create a 6/1 green Insect creature token with shroud. (It can't be the target of spells or abilities.)

Gluttonous Slug

Menace
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Mana Skimmer

Flying
Whenever Mana Skimmer deals damage to a player, tap target land that player controls. That land doesn't untap during its controller's next untap step.

Spire Mangler

Flash
Flying
When Spire Mangler enters, target creature you control with flying gets +2/+0 until end of turn.