Nahiri's Wrath

As an additional cost to cast this spell, discard X cards.
Nahiri's Wrath deals damage equal to the total mana value of the discarded cards to each of up to X target creatures and/or planeswalkers.

Iron Maiden

At the beginning of each opponent's upkeep, Iron Maiden deals X damage to that player, where X is the number of cards in their hand minus 4.

Oath of Jace

When Oath of Jace enters, draw three cards, then discard two cards.
At the beginning of your upkeep, scry X, where X is the number of planeswalkers you control.

Overmaster

The next instant or sorcery spell you cast this turn can't be countered.
Draw a card.

Spin into Myth

Put target creature on top of its owner's library, then fateseal 2. (To fateseal 2, look at the top two cards of an opponent's library, then put any number of them on the bottom of that player's library and the rest on top in any order.)

Telepathy

Your opponents play with their hands revealed.

Collective Defiance

Escalate {1} (Pay this cost for each mode chosen beyond the first.)
Choose one or more —
• Target player discards all the cards in their hand, then draws that many cards.
• Collective Defiance deals 4 damage to target creature.
• Collective Defiance deals 3 damage to target opponent or planeswalker.

Fevered Visions

At the beginning of each player's end step, that player draws a card. If the player is your opponent and has four or more cards in hand, Fevered Visions deals 2 damage to that player.

Inzerva, Master of Insights

+2: Draw two cards, then discard a card.
−2: Look at the top two cards of each other player's library, then put any number of them on the bottom of that library and the rest on top in any order. Scry 2.
−4: You get an emblem with "Your opponents play with their hands revealed" and "Whenever an opponent draws a card, this emblem deals 1 damage to them."

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Stormbreath Dragon

Flying, haste, protection from white
{5}{R}{R}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)
When Stormbreath Dragon becomes monstrous, it deals damage to each opponent equal to the number of cards in that player's hand.

Library of Leng

You have no maximum hand size.
If an effect causes you to discard a card, discard it, but you may put it on top of your library instead of into your graveyard.

Mountain

Sturmgeist

Flying
Sturmgeist's power and toughness are each equal to the number of cards in your hand.
Whenever Sturmgeist deals combat damage to a player, draw a card.

Sudden Impact

Sudden Impact deals damage to target player equal to the number of cards in that player's hand.

Nin, the Pain Artist

{X}{U}{R}, {T}: Nin, the Pain Artist deals X damage to target creature. That creature's controller draws X cards.

Dragon Mage

Flying
Whenever Dragon Mage deals combat damage to a player, each player discards their hand, then draws seven cards.

Spiraling Embers

Spiraling Embers deals damage to any target equal to the number of cards in your hand.

Viseling

At the beginning of each opponent's upkeep, Viseling deals X damage to that player, where X is the number of cards in their hand minus 4.

Folio of Fancies

Players have no maximum hand size.
{X}{X}, {T}: Each player draws X cards.
{2}{U}, {T}: Each opponent mills cards equal to the number of cards in their hand.

Windfall

Each player discards their hand, then draws cards equal to the greatest number of cards a player discarded this way.

Cerebral Vortex

Target player draws two cards, then Cerebral Vortex deals damage to that player equal to the number of cards they've drawn this turn.

Atemsis, All-Seeing

Flying
{2}{U}, {T}: Draw two cards, then discard a card.
Whenever Atemsis, All-Seeing deals damage to an opponent, you may reveal your hand. If cards with at least six different mana values are revealed this way, that player loses the game.

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.

Runeflare Trap

If an opponent drew three or more cards this turn, you may pay {R} rather than pay this spell's mana cost.
Runeflare Trap deals damage to target player equal to the number of cards in that player's hand.

Pulse of the Grid

Draw two cards, then discard a card. Then if an opponent has more cards in hand than you, return Pulse of the Grid to its owner's hand.

Niv-Mizzet, Parun

This spell can't be countered.
Flying
Whenever you draw a card, Niv-Mizzet, Parun deals 1 damage to any target.
Whenever a player casts an instant or sorcery spell, you draw a card.

Niv-Mizzet, the Firemind

Flying
Whenever you draw a card, Niv-Mizzet, the Firemind deals 1 damage to any target.
{T}: Draw a card.

Bag of Holding

Whenever you discard a card, exile that card from your graveyard.
{2}, {T}: Draw a card, then discard a card.
{4}, {T}, Sacrifice Bag of Holding: Return all cards exiled with Bag of Holding to their owner's hand.

Island

Glint-Horn Buccaneer

Haste
Whenever you discard a card, Glint-Horn Buccaneer deals 1 damage to each opponent.
{1}{R}, Discard a card: Draw a card. Activate only if Glint-Horn Buccaneer is attacking.

Psychosis Crawler

Psychosis Crawler's power and toughness are each equal to the number of cards in your hand.
Whenever you draw a card, each opponent loses 1 life.

Misers' Cage

At the beginning of each opponent's upkeep, if that player has five or more cards in hand, Misers' Cage deals 2 damage to that player.

Fateful Showdown

Fateful Showdown deals damage to any target equal to the number of cards in your hand. Discard all the cards in your hand, then draw that many cards.

Elixir of Immortality

{2}, {T}: You gain 5 life. Shuffle Elixir of Immortality and your graveyard into their owner's library.

Gaze of Adamaro

Gaze of Adamaro deals damage to target player equal to the number of cards in that player's hand.

Improbable Alliance

Whenever you draw your second card each turn, create a 1/1 blue Faerie creature token with flying.
{4}{U}{R}: Draw a card, then discard a card.

Thundering Djinn

Flying
Whenever Thundering Djinn attacks, it deals damage to any target equal to the number of cards you've drawn this turn.

Ebony Owl Netsuke

At the beginning of each opponent's upkeep, if that player has seven or more cards in hand, Ebony Owl Netsuke deals 4 damage to that player.