Bone Splinters

As an additional cost to cast this spell, sacrifice a creature.
Destroy target creature.

Essence Scatter

Don't Make a Sound

Counter target spell unless its controller pays {2}. If they do, surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Quick-Draw Katana

During your turn, equipped creature gets +2/+0 and has first strike. (It deals combat damage before creatures without first strike.)
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Buried Alive

Search your library for up to three creature cards, put them into your graveyard, then shuffle.

Assassin Den

Defender (This creature can't attack.)
{3}{U}: Put a +1/+1 counter on target creature you control. It can't be blocked this turn. Activate only as a sorcery.

Macabre Waltz

Return up to two target creature cards from your graveyard to your hand, then discard a card.

Roshan, Hidden Magister

Other creatures you control are Assassins in addition to their other types. The same is true for creature spells you control and creature cards you own that aren't on the battlefield.
Face-down creatures you control have menace.
Whenever a permanent you control is turned face up, you draw a card and you lose 1 life.

Evie Frye

Partner with Jacob Frye (When this creature enters, target player may put Jacob into their hand from their library, then shuffle.)
{1}, {T}: Draw a card, then discard a card. When you discard a creature card this way, target creature you control can't be blocked this turn.

Negate

The Revelations of Ezio

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Destroy target tapped creature an opponent controls.
II — Whenever an Assassin you control attacks this turn, put a +1/+1 counter on it.
III — Return target Assassin creature card from your graveyard to the battlefield with an additional +1/+1 counter on it.

Murder

Assassinate

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Lydia Frye

Lydia Frye can't be blocked by creatures with power 3 or greater.
At the beginning of your end step, surveil X, where X is the number of tapped Assassins you control. (Look at the top X cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Assassin Initiate

{1}: Assassin Initiate gains your choice of flying, deathtouch, or lifelink until end of turn.

Eagle Vision

Freerunning {1}{U} (You may cast this spell for its freerunning cost if you dealt combat damage to a player this turn with an Assassin or commander.)
Draw three cards.

Hired Blade

Flash (You may cast this spell any time you could cast an instant.)

Shakedown Heavy

Menace
Whenever Shakedown Heavy attacks, defending player may have you draw a card. If they do, untap Shakedown Heavy and remove it from combat.

Commune with Evil

Look at the top four cards of your library. Put one of them into your hand and the rest into your graveyard. You gain 3 life.

Brotherhood Ambushers

Freerunning {3}{B} (You may cast this spell for its freerunning cost if you dealt combat damage to a player this turn with an Assassin or commander.)

Jacob Frye

Partner with Evie Frye (When this creature enters, target player may put Evie into their hand from their library, then shuffle.)
Whenever one or more Assassins you control deal combat damage to a player, exile up to one target Assassin card or card with freerunning from your graveyard. If you do, copy it. You may cast the copy.

Petty Larceny

Freerunning {1}{B} (You may cast this spell for its freerunning cost if you dealt combat damage to a player this turn with an Assassin or commander.)
Look at the top two cards of target opponent's library and exile those cards face down. You may play those cards for as long as they remain exiled, and mana of any type can be spent to cast them. Create a Treasure token.