Confirmed

Arthur, Marigold Knight

Haste
Whenever Arthur, Marigold Knight and at least one other creature attack, look at the top six cards of your library. You may put a creature card from among them onto the battlefield tapped and attacking. Put the rest on the bottom of your library in a random order. Return that creature to its owner's hand at end of combat.

Mabel, Heir to Cragflame

Other Mice you control get +1/+1.
When Mabel, Heir to Cragflame enters, create Cragflame, a legendary colorless Equipment artifact token with "Equipped creature gets +1/+1 and has vigilance, trample, and haste" and equip {2}.

Port Razer

Whenever Port Razer deals combat damage to a player, untap each creature you control. After this phase, there is an additional combat phase.
Port Razer can't attack a player it has already attacked this turn.

Perilous Landscape

{T}: Add {C}.
{T}, Sacrifice Perilous Landscape: Search your library for a basic Island, Mountain, or Plains card, put it onto the battlefield tapped, then shuffle.
Cycling {U}{R}{W} ({U}{R}{W}, Discard this card: Draw a card.)

Medomai the Ageless

Flying
Whenever Medomai the Ageless deals combat damage to a player, take an extra turn after this one.
Medomai the Ageless can't attack during extra turns.

Chaos Warp

The owner of target permanent shuffles it into their library, then reveals the top card of their library. If it's a permanent card, they put it onto the battlefield.

Beza, the Bounding Spring

When Beza, the Bounding Spring enters, create a Treasure token if an opponent controls more lands than you. You gain 4 life if an opponent has more life than you. Create two 1/1 blue Fish creature tokens if an opponent controls more creatures than you. Draw a card if an opponent has more cards in hand than you.

Jacked Rabbit

Ravenous (This creature enters with X +1/+1 counters on it. If X is 5 or more, draw a card when it enters.)
Whenever Jacked Rabbit attacks, create a number of 1/1 white Rabbit creature tokens equal to Jacked Rabbit's power.

Lifecreed Duo

Flying
Whenever another creature you control enters, you gain 1 life.

Luminous Broodmoth

Flying
Whenever a creature you control without flying dies, return it to the battlefield under its owner's control with a flying counter on it.

Repel Calamity

Destroy target creature with power or toughness 4 or greater.

Riot Control

You gain 1 life for each creature your opponents control. Prevent all damage that would be dealt to you this turn.

Azure Beastbinder

Vigilance
Azure Beastbinder can't be blocked by creatures with power 2 or greater.
Whenever Azure Beastbinder attacks, up to one target artifact, creature, or planeswalker an opponent controls loses all abilities until your next turn. If it's a creature, it also has base power and toughness 2/2 until your next turn.

Eddymurk Crab

Flash
This spell costs {1} less to cast for each instant and sorcery card in your graveyard.
Eddymurk Crab enters tapped if it's not your turn.
When Eddymurk Crab enters, tap up to two target creatures.

Mind Spiral

Gift a tapped Fish (You may promise an opponent a gift as you cast this spell. If you do, they create a tapped 1/1 blue Fish creature token before its other effects.)
Target player draws three cards. If the gift was promised, tap target creature an opponent controls and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Splash Lasher

Offspring {1}{U} (You may pay an additional {1}{U} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
When this creature enters, tap up to one target creature and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Berserkers' Onslaught

Attacking creatures you control have double strike.

Gratuitous Violence

If a creature you control would deal damage to a permanent or player, it deals double that damage to that permanent or player instead.

Warstorm Surge

Whenever a creature you control enters, it deals damage equal to its power to any target.

Plains

Mountain

Island

Claim Jumper

Vigilance
When Claim Jumper enters, if an opponent controls more lands than you, you may search your library for a Plains card and put it onto the battlefield tapped. Then if an opponent controls more lands than you, repeat this process once. If you search your library this way, shuffle.

Éowyn, Fearless Knight

Haste
When Éowyn, Fearless Knight enters, exile target creature an opponent controls with greater power. Legendary creatures you control gain protection from each of that creature's colors until end of turn.

Moonshaker Cavalry

Flying
When Moonshaker Cavalry enters, creatures you control gain flying and get +X/+X until end of turn, where X is the number of creatures you control.

Meteor Golem

When Meteor Golem enters, destroy target nonland permanent an opponent controls.

Ilharg, the Raze-Boar

Trample
Whenever Ilharg, the Raze-Boar attacks, you may put a creature card from your hand onto the battlefield tapped and attacking. Return that creature to your hand at the beginning of the next end step.
When Ilharg, the Raze-Boar dies or is put into exile from the battlefield, you may put it into its owner's library third from the top.

Karmic Guide

Flying, protection from black
Echo {3}{W}{W} (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When Karmic Guide enters, return target creature card from your graveyard to the battlefield.

Aragorn, King of Gondor

Vigilance, lifelink
When Aragorn, King of Gondor enters, you become the monarch.
Whenever Aragorn attacks, up to one target creature can't block this turn. If you're the monarch, creatures can't block this turn.

Bloodthirster

Flying, trample
Whenever Bloodthirster deals combat damage to a player, untap it. After this phase, there is an additional combat phase.
Bloodthirster can't attack a player it has already attacked this turn.

Ponder

Look at the top three cards of your library, then put them back in any order. You may shuffle.
Draw a card.

Panharmonicon

If an artifact or creature entering causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Mithril Coat

Flash
Indestructible
When Mithril Coat enters, attach it to target legendary creature you control.
Equipped creature has indestructible.
Equip {3}

Cathars' Crusade

Whenever a creature you control enters, put a +1/+1 counter on each creature you control.

Reliquary Tower

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

Sol Ring

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Azorius Signet

Boros Signet

Izzet Signet

Thought Vessel

Command Tower

Exotic Orchard

{T}: Add one mana of any color that a land an opponent controls could produce.

Clifftop Retreat

Clifftop Retreat enters tapped unless you control a Mountain or a Plains.
{T}: Add {R} or {W}.

Sulfur Falls

Sulfur Falls enters tapped unless you control an Island or a Mountain.
{T}: Add {U} or {R}.

Mystic Monastery

Mystic Monastery enters tapped.
{T}: Add {U}, {R}, or {W}.

Glacial Fortress

Glacial Fortress enters tapped unless you control a Plains or an Island.
{T}: Add {W} or {U}.

Temple of Epiphany

Temple of Epiphany enters tapped.
When Temple of Epiphany enters, scry 1.
{T}: Add {U} or {R}.

Temple of Triumph

Temple of Triumph enters tapped.
When Temple of Triumph enters, scry 1.
{T}: Add {R} or {W}.

Fabled Passage

{T}, Sacrifice Fabled Passage: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Then if you control four or more lands, untap that land.

Port Town

As Port Town enters, you may reveal a Plains or Island card from your hand. If you don't, Port Town enters tapped.
{T}: Add {W} or {U}.

Cascade Bluffs

{T}: Add {C}.
{U/R}, {T}: Add {U}{U}, {U}{R}, or {R}{R}.

Skycloud Expanse

Azorius Chancery

Azorius Chancery enters tapped.
When Azorius Chancery enters, return a land you control to its owner's hand.
{T}: Add {W}{U}.

Velomachus Lorehold

Flying, vigilance, haste
Whenever Velomachus Lorehold attacks, look at the top seven cards of your library. You may cast an instant or sorcery spell with mana value less than or equal to Velomachus Lorehold's power from among them without paying its mana cost. Put the rest on the bottom of your library in a random order.

Brave the Sands

Creatures you control have vigilance.
Each creature you control can block an additional creature each combat.

Moraug, Fury of Akoum

Each creature you control gets +1/+0 for each time it has attacked this turn.
Landfall — Whenever a land you control enters, if it's your main phase, there's an additional combat phase after this phase. At the beginning of that combat, untap all creatures you control.

Aurelia, the Warleader

Flying, vigilance, haste
Whenever Aurelia, the Warleader attacks for the first time each turn, untap all creatures you control. After this phase, there is an additional combat phase.

Savage Beating

Cast this spell only during your turn and only during combat.
Choose one —
• Creatures you control gain double strike until end of turn.
• Untap all creatures you control. After this phase, there is an additional combat phase.
Entwine {1}{R} (Choose both if you pay the entwine cost.)

Unexpected Windfall

As an additional cost to cast this spell, discard a card.
Draw two cards and create two Treasure tokens. (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Brainstorm

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

Curse of the Swine

Exile X target creatures. For each creature exiled this way, its controller creates a 2/2 green Boar creature token.

Solemn Simulacrum

When Solemn Simulacrum enters, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.
When Solemn Simulacrum dies, you may draw a card.

Sun Titan

Vigilance
Whenever Sun Titan enters or attacks, you may return target permanent card with mana value 3 or less from your graveyard to the battlefield.

Cut a Deal

Each opponent draws a card, then you draw a card for each opponent who drew a card this way.

Archaeomancer's Map

When Archaeomancer's Map enters, search your library for up to two basic Plains cards, reveal them, put them into your hand, then shuffle.
Whenever a land an opponent controls enters, if that player controls more lands than you, you may put a land card from your hand onto the battlefield.

Quicksilver Amulet

{4}, {T}: You may put a creature card from your hand onto the battlefield.

Scroll Rack

{1}, {T}: Exile any number of cards from your hand face down. Put that many cards from the top of your library into your hand. Then look at the exiled cards and put them on top of your library in any order.

Angel of the Ruins

Flying
When Angel of the Ruins enters, exile up to two target artifacts and/or enchantments.
Plainscycling {2} ({2}, Discard this card: Search your library for a Plains card, reveal it, put it into your hand, then shuffle.)

Chivalric Alliance

Whenever you attack with two or more creatures, draw a card.
{2}, Discard a card: Create a 2/2 white and blue Knight creature token with vigilance.

Eagle of Deliverance

Flying
When Eagle of Deliverance enters, put an indestructible counter on another target creature you control. Draw a card if that creature's power is 2 or less.

Odric, Lunarch Marshal

At the beginning of each combat, creatures you control gain first strike until end of turn if a creature you control has first strike. The same is true for flying, deathtouch, double strike, haste, hexproof, indestructible, lifelink, menace, reach, skulk, trample, and vigilance.

Brago, King Eternal

Flying
Whenever Brago, King Eternal deals combat damage to a player, exile any number of target nonland permanents you control, then return those cards to the battlefield under their owner's control.

Reflector Mage

When Reflector Mage enters, return target creature an opponent controls to its owner's hand. That creature's owner can't cast spells with the same name as that creature until your next turn.

Brainsurge

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

Peregrine Drake

Flying
When Peregrine Drake enters, untap up to five lands.

Skyclave Apparition

When Skyclave Apparition enters, exile up to one target nonland, nontoken permanent you don't control with mana value 4 or less.
When Skyclave Apparition leaves the battlefield, the exiled card's owner creates an X/X blue Illusion creature token, where X is the mana value of the exiled card.

Sneak Attack

{R}: You may put a creature card from your hand onto the battlefield. That creature gains haste. Sacrifice the creature at the beginning of the next end step.

Pondering Mage

When Pondering Mage enters, look at the top three cards of your library, then put them back in any order. You may shuffle. Draw a card.

Reconnaissance

{0}: Remove target attacking creature you control from combat and untap it. (If you activate during end of combat, the creature will untap after it deals combat damage.)

Unbreakable Formation

Creatures you control gain indestructible until end of turn.
Addendum — If you cast this spell during your main phase, put a +1/+1 counter on each of those creatures and they gain vigilance until end of turn.

Impact Tremors

Whenever a creature you control enters, Impact Tremors deals 1 damage to each opponent.

Mirage Mesa

Mirage Mesa enters tapped. As it enters, choose a color.
{T}: Add one mana of the chosen color.