Opposition Agent

Flash
You control your opponents while they're searching their libraries.
While an opponent is searching their library, they exile each card they find. You may play those cards for as long as they remain exiled, and you may spend mana as though it were mana of any color to cast them.

Nirkana Revenant

Whenever you tap a Swamp for mana, add an additional {B}.
{B}: Nirkana Revenant gets +1/+1 until end of turn.

Thoughtseize

Target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

Mikaeus, the Unhallowed

Intimidate (This creature can't be blocked except by artifact creatures and/or creatures that share a color with it.)
Whenever a Human deals damage to you, destroy it.
Other non-Human creatures you control get +1/+1 and have undying. (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.)

Rush of Dread

Spree (Choose one or more additional costs.)
+ {1} — Target opponent sacrifices half the creatures they control, rounded up.
+ {2} — Target opponent discards half the cards in their hand, rounded up.
+ {2} — Target opponent loses half their life, rounded up.

Tergrid's Lantern

{T}: Target player loses 3 life unless they sacrifice a nonland permanent or discard a card.
{3}{B}: Untap Tergrid's Lantern.

Tergrid, God of Fright

Menace
Whenever an opponent sacrifices a nontoken permanent or discards a permanent card, you may put that card from a graveyard onto the battlefield under your control.

Tergrid, God of Fright // Tergrid's Lantern

Magus of the Coffers

{2}, {T}: Add {B} for each Swamp you control.

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this turn.

V.A.T.S.

Split second (As long as this spell is on the stack, players can't cast spells or activate abilities that aren't mana abilities.)
Choose any number of target creatures with equal toughness. Destroy the chosen creatures.

Bottomless Pit

At the beginning of each player's upkeep, that player discards a card at random.

Sanguine Bond

Whenever you gain life, target opponent loses that much life.

Sheoldred, the Apocalypse

Deathtouch
Whenever you draw a card, you gain 2 life.
Whenever an opponent draws a card, they lose 2 life.

Cabal Coffers

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}.

Polluted Bonds

Whenever a land an opponent controls enters, that player loses 2 life and you gain 2 life.

Death Cloud

Each player loses X life, discards X cards, sacrifices X creatures, then sacrifices X lands.

Cabal Stronghold

{T}: Add {C}.
{3}, {T}: Add {B} for each basic Swamp you control.

The Eldest Reborn

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Each opponent sacrifices a creature or planeswalker.
II — Each opponent discards a card.
III — Put target creature or planeswalker card from a graveyard onto the battlefield under your control.

Tinybones, the Pickpocket

Deathtouch
Whenever Tinybones, the Pickpocket deals combat damage to a player, you may cast target nonland permanent card from that player's graveyard, and mana of any type can be spent to cast that spell.

Soul Shatter

Each opponent sacrifices a creature or planeswalker with the highest mana value among creatures and planeswalkers they control.

Dark Deal

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

Tinybones Joins Up

When Tinybones Joins Up enters, any number of target players each discard a card.
Whenever a legendary creature you control enters, any number of target players each mill a card and lose 1 life.

Torment of Hailfire

Repeat the following process X times. Each opponent loses 3 life unless that player sacrifices a nonland permanent or discards a card.

Demon's Disciple

When Demon's Disciple enters, each player sacrifices a creature or planeswalker.

Liliana of the Veil

+1: Each player discards a card.
−2: Target player sacrifices a creature.
−6: Separate all permanents target player controls into two piles. That player sacrifices all permanents in the pile of their choice.

Liliana, Waker of the Dead

+1: Each player discards a card. Each opponent who can't loses 3 life.
−3: Target creature gets -X/-X until end of turn, where X is the number of cards in your graveyard.
−7: You get an emblem with "At the beginning of combat on your turn, put target creature card from a graveyard onto the battlefield under your control. It gains haste."

Mire in Misery

Each opponent sacrifices a creature or enchantment.

Oppression

Whenever a player casts a spell, that player discards a card.

Virus Beetle

When Virus Beetle enters, each opponent discards a card.

Geier Reach Sanitarium

{T}: Add {C}.
{2}, {T}: Each player draws a card, then discards a card.

Exquisite Blood

Whenever an opponent loses life, you gain that much life.

Syphon Mind

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