Queen Marchesa

Deathtouch, haste
When Queen Marchesa enters, you become the monarch.
At the beginning of your upkeep, if an opponent is the monarch, create a 1/1 black Assassin creature token with deathtouch and haste.

Callidus Assassin

Flash
Polymorphine — You may have this creature enter tapped as a copy of any creature on the battlefield, except it has "When this creature enters, destroy up to one other target creature with the same name as this creature."

King's Assassin

{T}: Destroy target tapped creature. Activate only during your turn, before attackers are declared.

Lurking Deadeye

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

Nekrataal

First strike
When this creature enters, destroy target nonartifact, nonblack creature. That creature can't be regenerated.

Vein Ripper

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

Altaïr Ibn-La'Ahad

First strike
Whenever Altaïr attacks, exile up to one target Assassin creature card from your graveyard with a memory counter on it. Then for each creature card you own in exile with a memory counter on it, create a tapped and attacking token that's a copy of it. Exile those tokens at end of combat.

Xira, the Golden Sting

Flying, haste
Whenever Xira attacks, put an egg counter on another target creature without an egg counter on it. When that creature dies, if it has an egg counter on it, draw a card and create a 1/1 black Insect creature token with flying.

Moritte of the Frost

Changeling (This card is every creature type.)
You may have Moritte enter as a copy of a permanent you control, except it's legendary and snow in addition to its other types and, if it's a creature, it enters with two additional +1/+1 counters on it and has changeling.

Twinblade Assassins

At the beginning of your end step, if a creature died this turn, draw a card.

Murderous Redcap

When this creature enters, it deals damage equal to its power to any target.
Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its owner's control with a -1/-1 counter on it.)

Thraximundar

Haste
Whenever Thraximundar attacks, defending player sacrifices a creature of their choice.
Whenever a player sacrifices a creature, you may put a +1/+1 counter on Thraximundar.

Taurean Mauler

Changeling (This card is every creature type.)
Whenever an opponent casts a spell, you may put a +1/+1 counter on this creature.

Ezio Auditore da Firenze

Menace
Assassin spells you cast have freerunning {B}{B}. (You may cast a spell for its freerunning cost if you dealt combat damage to a player this turn with an Assassin or commander.)
Whenever Ezio deals combat damage to a player, you may pay {W}{U}{B}{R}{G} if that player has 10 or less life. When you do, that player loses the game.

Royal Assassin

Wei Assassins

When this creature enters, target opponent chooses a creature they control. Destroy that creature.

Massacre Girl, Known Killer

Menace
Creatures you control have wither. (They deal damage to creatures in the form of -1/-1 counters.)
Whenever a creature an opponent controls dies, if its toughness was less than 1, draw a card.

Ezio, Blade of Vengeance

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
Whenever an Assassin you control deals combat damage to a player, draw a card.

Serpent Assassin

When this creature enters, you may destroy target nonblack creature.

Etrata, the Silencer

Etrata can't be blocked.
Whenever Etrata deals combat damage to a player, exile target creature that player controls and put a hit counter on that card. That player loses the game if they own three or more exiled cards with hit counters on them. Etrata's owner shuffles Etrata into their library.

Abyssal Hunter

{B}, {T}: Tap target creature. This creature deals damage equal to its power to that creature.

Mari, the Killing Quill

Whenever a creature an opponent controls dies, exile it with a hit counter on it.
Assassins, Mercenaries, and Rogues you control have deathtouch and "Whenever this creature deals combat damage to a player, you may remove a hit counter from a card that player owns in exile. If you do, draw a card and create two Treasure tokens."

Massacre Girl

Menace
When Massacre Girl enters, each other creature gets -1/-1 until end of turn. Whenever a creature dies this turn, each creature other than Massacre Girl gets -1/-1 until end of turn.

Thorn of the Black Rose

Deathtouch
When this creature enters, you become the monarch.

Ramses, Assassin Lord

Deathtouch
Other Assassins you control get +1/+1.
Whenever a player loses the game, if they were attacked this turn by an Assassin you controlled, you win the game.

Darkblade Agent

As long as you've surveilled this turn, this creature has deathtouch and "Whenever this creature deals combat damage to a player, you draw a card."

Graveshifter

Changeling (This card is every creature type.)
When this creature enters, you may return target creature card from your graveyard to your hand.

Final-Sting Faerie

Flying
When this creature enters, destroy target creature that was dealt damage this turn.

Stingblade Assassin

Flash
Flying
When this creature enters, destroy target creature an opponent controls that was dealt damage this turn.