Sivriss, Nightmare Speaker

{T}, Sacrifice another creature or an artifact: For each opponent, you mill a card, then return that card from your graveyard to your hand unless that player pays 3 life. (To mill a card, put the top card of your library into your graveyard.)
Choose a Background (You can have a Background as a second commander.)

Crypt Ghast

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever you tap a Swamp for mana, add an additional {B}.

One Ring to Rule Them All

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — The Ring tempts you, then each player mills cards equal to your Ring-bearer's power.
II — Destroy all nonlegendary creatures.
III — Each opponent loses 1 life for each creature card in that player's graveyard.

Grisly Spectacle

Destroy target nonartifact creature. Its controller mills cards equal to that creature's power.

The True Scriptures

(As this Saga enters and after your draw step, add a lore counter.)
I — For each opponent, destroy up to one target creature or planeswalker that player controls.
II — Each opponent discards three cards, then mills three cards.
III — Put all creature cards from all graveyards onto the battlefield under your control. Exile The True Scriptures, then return it to the battlefield (front face up).

Sheoldred

Menace
When Sheoldred enters, each opponent sacrifices a nontoken creature or planeswalker of their choice.
{4}{B}: Exile Sheoldred, then return it to the battlefield transformed under its owner's control. Activate only as a sorcery and only if an opponent has eight or more cards in their graveyard.

Sheoldred // The True Scriptures

Golgari Thug

When Golgari Thug dies, put target creature card from your graveyard on top of your library.
Dredge 4 (If you would draw a card, you may mill four cards instead. If you do, return this card from your graveyard to your hand.)

Dreadhound

When Dreadhound enters, mill three cards. (Put the top three cards of your library into your graveyard.)
Whenever a creature dies or a creature card is put into a graveyard from a library, each opponent loses 1 life.

Bubbling Muck

Until end of turn, whenever a player taps a Swamp for mana, that player adds an additional {B}.

Eye Collector

Flying
Whenever Eye Collector deals combat damage to a player, each player mills a card. (Each player puts the top card of their library into their graveyard.)

Reanimate

Put target creature card from a graveyard onto the battlefield under your control. You lose life equal to its mana value.

Corpse Churn

Mill three cards, then you may return a creature card from your graveyard to your hand. (To mill three cards, put the top three cards of your library into your graveyard.)

Supernatural Stamina

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control."

Mindcrank

Whenever an opponent loses life, that player mills that many cards. (Damage causes loss of life.)

Merciless Executioner

When Merciless Executioner enters, each player sacrifices a creature of their choice.

Village Rites

As an additional cost to cast this spell, sacrifice a creature.
Draw two cards.

Dark Deal

Each player discards all the cards in their hand, then draws that many cards minus one.

Dread Summons

Each player mills X cards. For each creature card put into a graveyard this way, you create a tapped 2/2 black Zombie creature token. (To mill a card, a player puts the top card of their library into their graveyard.)

Angel of Suffering

Flying
If damage would be dealt to you, prevent that damage and mill twice that many cards.

Gravelighter

Flying
When Gravelighter enters, draw a card if a creature died this turn. Otherwise, each player sacrifices a creature of their choice.

Feign Death

Until end of turn, target creature gains "When this creature dies, return it to the battlefield tapped under its owner's control with a +1/+1 counter on it."

Syr Konrad, the Grim

Whenever another creature dies, or a creature card is put into a graveyard from anywhere other than the battlefield, or a creature card leaves your graveyard, Syr Konrad, the Grim deals 1 damage to each opponent.
{1}{B}: Each player mills a card. (They each put the top card of their library into their graveyard.)

Malakir Mire

Malakir Mire enters tapped.
{T}: Add {B}.

Malakir Rebirth

Choose target creature. You lose 2 life. Until end of turn, that creature gains "When this creature dies, return it to the battlefield tapped under its owner's control."

Malakir Rebirth // Malakir Mire

Murderous Cut

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Destroy target creature.

Songs of the Damned

Add {B} for each creature card in your graveyard.

Leaden Myr

Shared Trauma

Join forces — Starting with you, each player may pay any amount of mana. Each player mills X cards, where X is the total amount of mana paid this way.

Cabal Ritual

Add {B}{B}{B}.
Threshold — Add {B}{B}{B}{B}{B} instead if seven or more cards are in your graveyard.

Perpetual Timepiece

{T}: Mill two cards.
{2}, Exile Perpetual Timepiece: Shuffle any number of target cards from your graveyard into your library.

Stitcher's Supplier

When Stitcher's Supplier enters or dies, mill three cards. (Put the top three cards of your library into your graveyard.)

Pile On

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Destroy target creature or planeswalker. 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.)

Fleshbag Marauder

When Fleshbag Marauder enters, each player sacrifices a creature of their choice.

Undercity Informer

{1}, Sacrifice a creature: Target player reveals cards from the top of their library until they reveal a land card, then puts those cards into their graveyard.

Syphon Mind

Each other player discards a card. You draw a card for each card discarded this way.

Reassembling Skeleton

{1}{B}: Return this card from your graveyard to the battlefield tapped.

Breach the Multiverse

Each player mills ten cards. For each player, choose a creature or planeswalker card in that player's graveyard. Put those cards onto the battlefield under your control. Then each creature you control becomes a Phyrexian in addition to its other types.

Mindwrack Harpy

Flying
At the beginning of combat on your turn, each player mills three cards.

Altar of Dementia

Sacrifice a creature: Target player mills cards equal to the sacrificed creature's power.

Doom Whisperer

Flying, trample
Pay 2 life: 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.)

Dark Ritual

Returned Reveler

When Returned Reveler dies, each player mills three cards.

Millikin

{T}, Mill a card: Add {C}. (To mill a card, put the top card of your library into your graveyard.)

Buried Alive

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

Undead Butler

When Undead Butler enters, mill three cards. (Put the top three cards of your library into your graveyard.)
When Undead Butler dies, you may exile it. When you do, return target creature card from your graveyard to your hand.