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.

Silumgar Butcher

Exploit (When this creature enters, you may sacrifice a creature.)
When Silumgar Butcher exploits a creature, target creature gets -3/-3 until end of turn.

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.)

Undercity Scavenger

When Undercity Scavenger enters, you may sacrifice another creature. If you do, put two +1/+1 counters on Undercity Scavenger, then scry 2.

Thorn of the Black Rose

Deathtouch
When Thorn of the Black Rose enters, you become the monarch.

Seekers' Squire

When Seekers' Squire enters, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)

Spiderwig Boggart

When Spiderwig Boggart enters, target creature gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)

Cadaver Imp

Flying
When Cadaver Imp enters, you may return target creature card from your graveyard to your hand.

Diregraf Scavenger

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
When Diregraf Scavenger enters, exile up to one target card from a graveyard. If a creature card was exiled this way, each opponent loses 2 life and you gain 2 life.

Hooded Assassin

When Hooded Assassin enters, choose one —
• Put a +1/+1 counter on Hooded Assassin.
• Destroy target creature that was dealt damage this turn.

Shadow Alley Denizen

Whenever another black creature you control enters, target creature gains intimidate until end of turn. (It can't be blocked except by artifact creatures and/or creatures that share a color with it.)

Lurking Deadeye

Flash
When Lurking Deadeye enters, destroy target creature that was dealt damage this turn.

Fourth Bridge Prowler

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

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Diregraf Horde

When Diregraf Horde enters, create two 2/2 black Zombie creature tokens with decayed. When you do, exile up to two target cards from graveyards. (A creature with decayed can't block. When it attacks, sacrifice it at end of combat.)

Slum Reaper

When Slum Reaper enters, each player sacrifices a creature of their choice.

Vampire Spawn

When this creature enters, each opponent loses 2 life and you gain 2 life.

Mesmeric Fiend

When Mesmeric Fiend enters, target opponent reveals their hand and you choose a nonland card from it. Exile that card.
When Mesmeric Fiend leaves the battlefield, return the exiled card to its owner's hand.

Faceless Butcher

When Faceless Butcher enters, exile another target creature.
When Faceless Butcher leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Vulturous Aven

Flying
Exploit (When this creature enters, you may sacrifice a creature.)
When Vulturous Aven exploits a creature, you draw two cards and you lose 2 life.

Underdark Explorer

Menace (This creature can't be blocked except by two or more creatures.)
When Underdark Explorer enters, you take the initiative.

Rot-Tide Gargantua

Exploit (When this creature enters, you may sacrifice a creature.)
When Rot-Tide Gargantua exploits a creature, each opponent sacrifices a creature of their choice.

Courier Bat

Flying
When Courier Bat enters, if you gained life this turn, return up to one target creature card from your graveyard to your hand.

Orzhov Euthanist

Haunt (When this creature dies, exile it haunting target creature.)
When Orzhov Euthanist enters or the creature it haunts dies, destroy target creature that was dealt damage this turn.

Skull Collector

At the beginning of your upkeep, return a black creature you control to its owner's hand.
{1}{B}: Regenerate Skull Collector.

Clockwork Fox

When Clockwork Fox leaves the battlefield, you draw two cards and each opponent draws a card.

Wicked Guardian

When Wicked Guardian enters, you may have it deal 2 damage to another creature you control. If you do, draw a card.

Vicious Battlerager

When Vicious Battlerager enters, you take the initiative.
Spiked Retribution — Whenever Vicious Battlerager becomes blocked by a creature, that creature's controller loses 5 life.

Farfinder

Vigilance
When Farfinder enters, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle.