Acidic Slime

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
When Acidic Slime enters, destroy target artifact, enchantment, or land.

Biogenic Ooze

When Biogenic Ooze enters, create a 2/2 green Ooze creature token.
At the beginning of your end step, put a +1/+1 counter on each Ooze you control.
{1}{G}{G}{G}: Create a 2/2 green Ooze creature token.

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.

Giant Cockroach

Endless Cockroaches

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

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.

Gluttonous Slime

Flash
Devour 1 (As this enters, you may sacrifice any number of creatures. This creature enters with that many +1/+1 counters on it.)

Squelching Leeches

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

Primal Cocoon

Enchant creature
At the beginning of your upkeep, put a +1/+1 counter on enchanted creature.
When enchanted creature attacks or blocks, sacrifice Primal Cocoon.

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.)

Filth

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
As long as Filth is in your graveyard and you control a Swamp, creatures you control have swampwalk.

Catacomb Slug

Consumptive Goo

{2}{B}{B}: Target creature gets -1/-1 until end of turn. Put a +1/+1 counter on Consumptive Goo.

Slime Molding

Blitz Leech

Flash
When Blitz Leech enters, target creature an opponent controls gets -2/-2 until end of turn. Remove all counters from that creature.

Spitting Slug

Whenever Spitting Slug blocks or becomes blocked, you may pay {1}{G}. If you do, Spitting Slug gains first strike until end of turn. Otherwise, each creature blocking or blocked by Spitting Slug gains first strike until end of turn.

Miming Slime

Create an X/X green Ooze creature token, where X is the greatest power among creatures you control.

Putrid Leech

Pay 2 life: Putrid Leech 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.

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.

Leeching Bite

Target creature gets +1/+1 until end of turn. Another target creature gets -1/-1 until end of turn.

Necroplasm

At the beginning of your upkeep, put a +1/+1 counter on Necroplasm.
At the beginning of your end step, destroy each creature with mana value equal to the number of +1/+1 counters on Necroplasm.
Dredge 2 (If you would draw a card, you may mill two cards instead. If you do, return this card from your graveyard to your hand.)

Creeping Mold

Destroy target artifact, enchantment, or land.

Giant Growth

Target creature gets +3/+3 until end of turn.

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.

Land Leeches

Insidious Bookworms

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

Ravenous Slime

Ravenous Slime can't be blocked by creatures with power 2 or less.
If a creature an opponent controls would die, instead exile it and put a number of +1/+1 counters equal to that creature's power on Ravenous Slime.

Heartstabber Mosquito

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