Fourth Bridge Prowler

When Fourth Bridge Prowler enters, you may have target creature get -1/-1 until end of turn.

Vault Plunderer

When Vault Plunderer enters, target player draws a card and loses 1 life.

Maggot Carrier

When Maggot Carrier enters, each player loses 1 life.

Boot Nipper

Boot Nipper enters with your choice of a deathtouch counter or a lifelink counter on it.

Brink of Disaster

Enchant creature or land
When enchanted permanent becomes tapped, destroy it.

Cauldron Familiar

When Cauldron Familiar enters, each opponent loses 1 life and you gain 1 life.
Sacrifice a Food: Return Cauldron Familiar from your graveyard to the battlefield.

Burglar Rat

When Burglar Rat enters, each opponent discards a card.

Desperate Bloodseeker

Lifelink
When Desperate Bloodseeker enters, target player mills two cards. (They put the top two cards of their library into their graveyard.)

Mardu Skullhunter

Mardu Skullhunter enters tapped.
Raid — When Mardu Skullhunter enters, if you attacked this turn, target opponent discards a card.

Gloomfang Mauler

Swampcycling {2} ({2}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)
Backup 2 (When this creature enters, put two +1/+1 counters on target creature. If that's another creature, it gains the following ability until end of turn.)
Menace

Corrupt Court Official

When Corrupt Court Official enters, target opponent discards a card.

Demon's Disciple

When Demon's Disciple enters, each player sacrifices a creature or planeswalker of their choice.

Troll of Khazad-dûm

Troll of Khazad-dûm can't be blocked except by three or more creatures.
Swampcycling {1} ({1}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Duskwalker

Kicker {3}{B} (You may pay an additional {3}{B} as you cast this spell.)
If Duskwalker was kicked, it enters with two +1/+1 counters on it and with fear. (It can't be blocked except by artifact creatures and/or black creatures.)

Twisted Abomination

{B}: Regenerate Twisted Abomination. (The next time this creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)
Swampcycling {2} ({2}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Balemurk Leech

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

Stronghold Confessor

Kicker {3} (You may pay an additional {3} as you cast this spell.)
Menace (This creature can't be blocked except by two or more creatures.)
If Stronghold Confessor was kicked, it enters with two +1/+1 counters on it.

Spectral Snatcher

Ward—Discard a card. (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player discards a card.)
Swampcycling {2} ({2}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Uruk-hai Berserker

When Uruk-hai Berserker enters, the Ring tempts you.

Quag Vampires

Multikicker {1}{B} (You may pay an additional {1}{B} any number of times as you cast this spell.)
Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
Quag Vampires enters with a +1/+1 counter on it for each time it was kicked.

Foul Imp

Flying
When Foul Imp enters, you lose 2 life.

Injector Crocodile

When Injector Crocodile dies, incubate 3. (Create an Incubator token with three +1/+1 counters on it and "{2}: Transform this artifact." It transforms into a 0/0 Phyrexian artifact creature.)
Swampcycling {2} ({2}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Chittering Rats

When Chittering Rats enters, target opponent puts a card from their hand on top of their library.

Crypt Rats

{X}: Crypt Rats deals X damage to each creature and each player. Spend only black mana on X.

Fleshbag Marauder

When Fleshbag Marauder enters, each player sacrifices a creature of their choice.

Sultai Scavenger

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Flying

Blood Seeker

Whenever a creature an opponent controls enters, you may have that player lose 1 life.

Blessing of Leeches

Flash
Enchant creature
At the beginning of your upkeep, you lose 1 life.
{0}: Regenerate enchanted creature.

Crooked Custodian

Gurmag Angler

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)