First strike

Whenever Altaïr Ibn-La'Ahad 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.

Flash

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

Lands you control have "{T}: Add one mana of any color."

{T}: Add one mana of any color.

As Cover of Darkness enters the battlefield, choose a creature type.

Creatures of the chosen type have fear. (They can't be blocked except by artifact creatures and/or black creatures.)

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.

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.

Deathtouch

When Guildsworn Prowler dies, if it wasn't blocking, draw a card.

Commander creatures you own have "Whenever this creature becomes tapped, it and other creatures you control that share a creature type with it each get +2/+0 and gain undying until end of turn." (When a creature with undying 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.)

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."

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.

Flying, lifelink

Whenever one or more outlaws you control deal combat damage to a player, create a Treasure token. (Assassins, Mercenaries, Pirates, Rogues, and Warlocks are outlaws.)

{3}, Sacrifice two Treasures: Put two +1/+1 counters on each creature you control. Activate only as a sorcery.

Deathtouch, haste

When Queen Marchesa enters the battlefield, 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.

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.

Ward {2}

As Roaming Throne enters the battlefield, choose a creature type.

Roaming Throne is the chosen type in addition to its other types.

If a triggered ability of another creature you control of the chosen type triggers, it triggers an additional time.

{T}: Destroy target tapped creature.

Flash

Flying

When Stingblade Assassin enters the battlefield, destroy target creature an opponent controls that was dealt damage this turn.

Equipped creature gets +1/+1.

Whenever equipped creature attacks, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Equip {2}

Changeling (This card is every creature type.)

Whenever an opponent casts a spell, you may put a +1/+1 counter on Taurean Mauler.

Deathtouch

Unleash (You may have this creature enter the battlefield with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)

Defender

{T}: Exchange target opponent's life total with Tree of Perdition's toughness.

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

Flying

Ward--Sacrifice a creature.

Whenever a creature dies, target opponent loses 2 life and you gain 2 life.

Partner with Gorm the Great (When this creature enters the battlefield, target player may put Gorm into their hand from their library, then shuffle.)

Deathtouch

Whenever Virtus the Veiled deals combat damage to a player, that player loses half their life, rounded up.

Deathtouch

Whenever a nontoken creature an opponent controls dies, you may pay {1}. If you do, return that card to the battlefield tapped under your control. It's a Treasure artifact with "{T}, Sacrifice this artifact: Add one mana of any color," and it loses all other card types.