Death Cloud

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

Mindslaver

{4}, {T}, Sacrifice Mindslaver: You control target player during that player's next turn. (You see all cards that player could see and make all decisions for the player.)

Mathas, Fiend Seeker

Menace
At the beginning of your end step, put a bounty counter on target creature an opponent controls. For as long as that creature has a bounty counter on it, it has "When this creature dies, each opponent draws a card and gains 2 life."

Mana Breach

Whenever a player casts a spell, that player returns a land they control to its owner's hand.

Braid of Fire

Cumulative upkeep—Add {R}. (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)

Sire of Insanity

At the beginning of each end step, each player discards their hand.

Narset, Enlightened Master

First strike, hexproof
Whenever Narset, Enlightened Master attacks, exile the top four cards of your library. Until end of turn, you may cast noncreature spells from among those cards without paying their mana costs.

Mass Manipulation

Gain control of X target creatures and/or planeswalkers.

Jinxed Idol

At the beginning of your upkeep, Jinxed Idol deals 2 damage to you.
Sacrifice a creature: Target opponent gains control of Jinxed Idol.

Jinxed Ring

Whenever a nontoken permanent is put into your graveyard from the battlefield, Jinxed Ring deals 1 damage to you.
Sacrifice a creature: Target opponent gains control of Jinxed Ring. (This effect lasts indefinitely.)

Winter Orb

As long as Winter Orb is untapped, players can't untap more than one land during their untap steps.

Witch Hunt

Players can't gain life.
At the beginning of your upkeep, Witch Hunt deals 4 damage to you.
At the beginning of your end step, target opponent chosen at random gains control of Witch Hunt.

Humble Defector

{T}: Draw two cards. Target opponent gains control of Humble Defector. Activate only during your turn.

Consecrated Sphinx

Flying
Whenever an opponent draws a card, you may draw two cards.

Sun Quan, Lord of Wu

Creatures you control have horsemanship. (They can't be blocked except by creatures with horsemanship.)

Treachery

Enchant creature
When Treachery enters, untap up to five lands.
You control enchanted creature.

Zedruu the Greathearted

At the beginning of your upkeep, you gain X life and draw X cards, where X is the number of permanents you own that your opponents control.
{U}{R}{W}: Target opponent gains control of target permanent you control.

Teferi's Protection

Until your next turn, your life total can't change and you gain protection from everything. All permanents you control phase out. (While they're phased out, they're treated as though they don't exist. They phase in before you untap during your untap step.)
Exile Teferi's Protection.

Back to Basics

Nonbasic lands don't untap during their controllers' untap steps.

Akroan Horse

Defender
When Akroan Horse enters, an opponent gains control of it.
At the beginning of your upkeep, each opponent creates a 1/1 white Soldier creature token.

Global Ruin

Each player chooses from the lands they control a land of each basic land type, then sacrifices the rest.

Memorial to Glory

Memorial to Glory enters tapped.
{T}: Add {W}.
{3}{W}, {T}, Sacrifice Memorial to Glory: Create two 1/1 white Soldier creature tokens.

Thoughts of Ruin

Each player sacrifices a land for each card in your hand.

Warp World

Each player shuffles all permanents they own into their library, then reveals that many cards from the top of their library. Each player puts all artifact, creature, and land cards revealed this way onto the battlefield, then does the same for enchantment cards, then puts all cards revealed this way that weren't put onto the battlefield on the bottom of their library.

Memorial to Folly

Memorial to Folly enters tapped.
{T}: Add {B}.
{2}{B}, {T}, Sacrifice Memorial to Folly: Return target creature card from your graveyard to your hand.

Bolas's Citadel

You may look at the top card of your library any time.
You may play lands and cast spells from the top of your library. If you cast a spell this way, pay life equal to its mana value rather than pay its mana cost.
{T}, Sacrifice ten nonland permanents: Each opponent loses 10 life.

Jin-Gitaxias, Core Augur

Flash
At the beginning of your end step, draw seven cards.
Each opponent's maximum hand size is reduced by seven.

Whims of the Fates

Starting with you, each player separates all permanents they control into three piles. Then each player chooses one of their piles at random and sacrifices those permanents. (Piles can be empty.)

Humility

All creatures lose all abilities and have base power and toughness 1/1.

Thieves' Auction

Exile all nontoken permanents. Starting with you, each player chooses one of the exiled cards and puts it onto the battlefield tapped under their control. Repeat this process until all cards exiled this way have been chosen.

Entrancing Melody

Gain control of target creature with mana value X.

Stasis

Players skip their untap steps.
At the beginning of your upkeep, sacrifice Stasis unless you pay {U}.

Aetherflux Reservoir

Whenever you cast a spell, you gain 1 life for each spell you've cast this turn.
Pay 50 life: Aetherflux Reservoir deals 50 damage to any target.

Tainted Aether

Whenever a creature enters, its controller sacrifices a creature or land.

Teferi's Puzzle Box

At the beginning of each player's draw step, that player puts the cards in their hand on the bottom of their library in any order, then draws that many cards.

Possessed Portal

If a player would draw a card, that player skips that draw instead.
At the beginning of each end step, each player sacrifices a permanent unless they discard a card.

Smokestack

At the beginning of your upkeep, you may put a soot counter on Smokestack.
At the beginning of each player's upkeep, that player sacrifices a permanent for each soot counter on Smokestack.

Citadel of Pain

At the beginning of each player's end step, Citadel of Pain deals X damage to that player, where X is the number of untapped lands they control.

Mystic Remora

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Omniscience

You may cast spells from your hand without paying their mana costs.

Jinxed Choker

At the beginning of your end step, target opponent gains control of Jinxed Choker and puts a charge counter on it.
At the beginning of your upkeep, Jinxed Choker deals damage to you equal to the number of charge counters on it.
{3}: Put a charge counter on Jinxed Choker or remove one from it.