Arvinox, the Mind Flail

Arvinox isn't a creature unless you control three or more permanents you don't own.
At the beginning of your end step, exile the bottom card of each opponent's library face down. For as long as those cards remain exiled, you may look at them, you may cast permanent spells from among them, and you may spend mana as though it were mana of any color to cast those spells.

Tecutlan, the Searing Rift

(Transforms from Brass's Tunnel-Grinder.)
{T}: Add {R}.
Whenever you cast a permanent spell using mana produced by Tecutlan, discover X, where X is that spell's mana value.

Brass's Tunnel-Grinder

When Brass's Tunnel-Grinder enters, discard any number of cards, then draw that many cards plus one.
At the beginning of your end step, if you descended this turn, put a bore counter on Brass's Tunnel-Grinder. Then if there are three or more bore counters on it, remove those counters and transform it. (You descended if a permanent card was put into your graveyard from anywhere.)

Brass's Tunnel-Grinder // Tecutlan, the Searing Rift

The Akroan War

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Gain control of target creature for as long as this Saga remains on the battlefield.
II — Until your next turn, creatures your opponents control attack each combat if able.
III — Each tapped creature deals damage to itself equal to its power.

Tasha, the Witch Queen

Whenever you cast a spell you don't own, create a 3/3 black Demon creature token.
+1: Draw a card. For each opponent, exile up to one target instant or sorcery card from that player's graveyard and put a page counter on it.
−3: You may cast a spell from among cards in exile with page counters on them without paying its mana cost.
Tasha, the Witch Queen can be your commander.

Lidless Gaze

Exile the top card of each player's library. Until the end of your next turn, you may play those cards, and mana of any type can be spent to cast those spells.
Flashback {2}{B}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Dire Blunderbuss

Equipped creature gets +3/+0 and has "Whenever this creature attacks, you may sacrifice an artifact other than Dire Blunderbuss. When you do, this creature deals damage equal to its power to target creature."
Equip {1}

Dire Flail

Equipped creature gets +2/+0.
Equip {1}
Craft with artifact {3}{R}{R} ({3}{R}{R}, Exile this artifact, Exile another artifact you control or an artifact card from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.)

Dire Flail // Dire Blunderbuss

Ramirez DePietro, Pillager

When Ramirez DePietro enters, you lose 2 life and create two Treasure tokens.
Whenever one or more Pirates you control deal combat damage to a player, exile the top card of that player's library. You may cast that card for as long as it remains exiled.

Mind Flayer

Dominate Monster — When this creature enters, gain control of target creature for as long as you control this creature.

Xanathar, Guild Kingpin

At the beginning of your upkeep, choose target opponent. Until end of turn, that player can't cast spells, you may look at the top card of their library any time, you may play the top card of their library, and you may spend mana as though it were mana of any color to cast spells this way.

Black Market Connections

At the beginning of your first main phase, choose one or more —
• Sell Contraband — Create a Treasure token. You lose 1 life.
• Buy Information — Draw a card. You lose 2 life.
• Hire a Mercenary — Create a 3/2 colorless Shapeshifter creature token with changeling. You lose 3 life. (It has every creature type.)

Ashiok, Nightmare Muse

+1: Create a 2/3 blue and black Nightmare creature token with "Whenever this token attacks or blocks, each opponent exiles the top two cards of their library."
−3: Return target nonland permanent to its owner's hand, then that player exiles a card from their hand.
−7: You may cast up to three spells from among face-up cards your opponents own from exile without paying their mana costs.

King Narfi's Betrayal

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Each player mills four cards. Then you may exile a creature or planeswalker card from each graveyard.
II, III — Until end of turn, you may cast spells from among cards exiled with this Saga, and you may spend mana as though it were mana of any color to cast those spells.

Rangers of Ithilien

Vigilance
When this creature enters, gain control of up to one target creature with lesser power for as long as you control this creature. Then the Ring tempts you.

Rogue Class

(Gain the next level as a sorcery to add its ability.)
Whenever a creature you control deals combat damage to a player, exile the top card of that player's library face down. You may look at it for as long as it remains exiled.
{1}{U}{B}: Level 2
Creatures you control have menace.
{2}{U}{B}: Level 3
You may play cards exiled with this Class, and you may spend mana as though it were mana of any color to cast those spells.

Don Andres, the Renegade

Each creature you control but don't own gets +2/+2, has menace and deathtouch, and is a Pirate in addition to its other types.
Whenever you cast a noncreature spell you don't own, create two tapped Treasure tokens.

Professional Face-Breaker

Menace
Whenever one or more creatures you control deal combat damage to a player, create a Treasure token.
Sacrifice a Treasure: Exile the top card of your library. You may play that card this turn.

Rise from the Grave

Put target creature card from a graveyard onto the battlefield under your control. That creature is a black Zombie in addition to its other colors and types.

Xander's Lounge

({T}: Add {U}, {B}, or {R}.)
This land enters tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

Talion, the Kindly Lord

Flying
As Talion enters, choose a number between 1 and 10.
Whenever an opponent casts a spell with mana value, power, or toughness equal to the chosen number, that player loses 2 life and you draw a card.

Umbris, Fear Manifest

Umbris gets +1/+1 for each card your opponents own in exile.
Whenever Umbris or another Nightmare or Horror you control enters, target opponent exiles cards from the top of their library until they exile a land card.

Admiral Brass, Unsinkable

When Admiral Brass enters, mill four cards.
At the beginning of combat on your turn, you may return target Pirate creature card from your graveyard to the battlefield with a finality counter on it. It has base power and toughness 4/4. It gains haste until end of turn. (If a creature with a finality counter on it would die, exile it instead.)

Hostile Takeover

Up to one target creature has base power and toughness 1/1 until end of turn. Up to one other target creature has base power and toughness 4/4 until end of turn. Then Hostile Takeover deals 3 damage to each creature.

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.")