Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Wandering Fumarole

Wandering Fumarole enters tapped.
{T}: Add {U} or {R}.
{2}{U}{R}: Until end of turn, Wandering Fumarole becomes a 1/4 blue and red Elemental creature with "{0}: Switch this creature's power and toughness until end of turn." It's still a land.

Pursued Whale

When Pursued Whale enters, each opponent creates a 1/1 red Pirate creature token with "This creature can't block" and "Creatures you control attack each combat if able."
Spells your opponents cast that target Pursued Whale cost {3} more to cast.

Chandra, Torch of Defiance

+1: Exile the top card of your library. You may cast that card. If you don't, Chandra, Torch of Defiance deals 2 damage to each opponent.
+1: Add {R}{R}.
−3: Chandra, Torch of Defiance deals 4 damage to target creature.
−7: You get an emblem with "Whenever you cast a spell, this emblem deals 5 damage to any target."

Alrund's Epiphany

Create two 1/1 blue Bird creature tokens with flying. Take an extra turn after this one. Exile Alrund's Epiphany.
Foretell {4}{U}{U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Island

Chain Reaction

Chain Reaction deals X damage to each creature, where X is the number of creatures on the battlefield.

Apocalypse

Exile all permanents. You discard your hand.

Command Tower

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

Scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Draw a card.

Aminatou's Augury

Exile the top eight cards of your library. You may put a land card from among them onto the battlefield. Until end of turn, for each nonland card type, you may cast a spell of that type from among the exiled cards without paying its mana cost.

Ankh of Mishra

Whenever a land enters, Ankh of Mishra deals 2 damage to that land's controller.

Avatar of Slaughter

All creatures have double strike and attack each combat if able.

Izzet Signet

Sol Ring

Aqueous Form

Enchant creature
Enchanted creature can't be blocked.
Whenever enchanted creature attacks, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Temple of Epiphany

This land enters tapped.
When this land enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
{T}: Add {U} or {R}.

Earth Tremor

Earth Tremor deals damage to target creature or planeswalker equal to the number of lands you control.

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

One with the Multiverse

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.
Once during each of your turns, you may cast a spell from your hand or the top of your library without paying its mana cost.

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.

Aether Gale

Return six target nonland permanents to their owners' hands.

Evacuation

Return all creatures to their owners' hands.

Vandalblast

Destroy target artifact you don't control.
Overload {4}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Devious Cover-Up

Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard. You may shuffle up to four target cards from your graveyard into your library.

Act of Treason

Gain control of target creature until end of turn. Untap that creature. It gains haste until end of turn. (It can attack and {T} this turn.)

Inspired Tinkering

Exile the top three cards of your library. Until the end of your next turn, you may play those cards.
Create three Treasure tokens. (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Preordain

Scry 2, then draw a card. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Reins of Power

Untap all creatures you control and all creatures target opponent controls. You and that opponent each gain control of all creatures the other controls until end of turn. Those creatures gain haste until end of turn.

Worldfire

Exile all permanents. Exile all cards from all hands and graveyards. Each player's life total becomes 1.

Paradise Plume

As Paradise Plume enters, choose a color.
Whenever a player casts a spell of the chosen color, you may gain 1 life.
{T}: Add one mana of the chosen color.

Arcane Signet

Aetherspouts

For each attacking creature, its owner puts it on their choice of the top or bottom of their library.

Propaganda

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Shock

Infuriate

Target creature gets +3/+2 until end of turn.

Star of Extinction

Destroy target land. Star of Extinction deals 20 damage to each creature and each planeswalker.

Otherworldly Gaze

Surveil 3. (Look at the top three cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)
Flashback {1}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Izzet Boilerworks

Izzet Boilerworks enters tapped.
When Izzet Boilerworks enters, return a land you control to its owner's hand.
{T}: Add {U}{R}.

Galestrike

Return target tapped creature to its owner's hand.
Draw a card.

Faithless Looting

Draw two cards, then discard two cards.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Archaeomancer

When Archaeomancer enters, return target instant or sorcery card from your graveyard to your hand.

Sprite Dragon

Flying, haste
Whenever you cast a noncreature spell, put a +1/+1 counter on Sprite Dragon.

Bearer of the Heavens

When Bearer of the Heavens dies, destroy all permanents at the beginning of the next end step.

Hullbreaker Horror

Flash
This spell can't be countered.
Whenever you cast a spell, choose up to one —
• Return target spell you don't control to its owner's hand.
• Return target nonland permanent to its owner's hand.

Seize the Spotlight

Each opponent chooses fame or fortune. For each player who chose fame, gain control of a creature that player controls until end of turn. Untap those creatures and they gain haste until end of turn. For each player who chose fortune, you draw a card and create a Treasure token.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice Mind Stone: Draw a card.

Obliterate

This spell can't be countered.
Destroy all artifacts, creatures, and lands. They can't be regenerated.

Ponder

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

Volcanic Awakening

Destroy target land.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Pillage

Destroy target artifact or land. It can't be regenerated.

Decanter of Endless Water

You have no maximum hand size.
{T}: Add one mana of any color.

Rewind

Counter target spell. Untap up to four lands.

Mizzix, Replica Rider

Flying
Whenever you cast a spell from anywhere other than your hand, you may pay {1}{U/R}. If you do, copy that spell and you may choose new targets for the copy. If the copy is a permanent spell, it gains haste and "At the beginning of your end step, sacrifice this permanent." (A copy of a permanent spell becomes a token.)

Sakashima of a Thousand Faces

You may have Sakashima of a Thousand Faces enter as a copy of another creature you control, except it has Sakashima of a Thousand Faces's other abilities.
The "legend rule" doesn't apply to permanents you control.
Partner (You can have two commanders if both have partner.)

Storm-Kiln Artist

Storm-Kiln Artist gets +1/+0 for each artifact you control.
Magecraft — Whenever you cast or copy an instant or sorcery spell, create a Treasure token.

Prismari Campus

Prismari Campus enters tapped.
{T}: Add {U} or {R}.
{4}, {T}: Scry 1.

Jokulhaups

Destroy all artifacts, creatures, and lands. They can't be regenerated.

Brainstorm

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

Rod of Absorption

Whenever a player casts an instant or sorcery spell, exile it instead of putting it into a graveyard as it resolves.
{X}, {T}, Sacrifice Rod of Absorption: You may cast any number of spells from among cards exiled with Rod of Absorption with total mana value X or less without paying their mana costs.

Fellwar Stone

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

Reliquary Tower

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

Ancient Silver Dragon

Flying
Whenever Ancient Silver Dragon deals combat damage to a player, roll a d20. Draw cards equal to the result. You have no maximum hand size for the rest of the game.

Counterspell

Scholar of the Ages

When Scholar of the Ages enters, return up to two target instant and/or sorcery cards from your graveyard to your hand.

Unwind

Counter target noncreature spell. Untap up to three lands.

Mountain

Bucknard's Everfull Purse

{1}, {T}: Roll a d4 and create a number of Treasure tokens equal to the result. The player to your right gains control of Bucknard's Everfull Purse.

Heartless Hidetsugu

{T}: Heartless Hidetsugu deals damage to each player equal to half that player's life total, rounded down.

Stitch in Time

Flip a coin. If you win the flip, take an extra turn after this one.

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.

Dissipation Field

Whenever a permanent deals damage to you, return it to its owner's hand.

Manabarbs

Whenever a player taps a land for mana, Manabarbs deals 1 damage to that player.

Wake of Destruction

Destroy target land and all other lands with the same name as that land.

Blood Moon

Heat Stroke

At end of combat, destroy each creature that blocked or was blocked this turn.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

Bond of Insight

Each player mills four cards. Return up to two instant and/or sorcery cards from your graveyard to your hand. Exile Bond of Insight.

Brass's Bounty

For each land you control, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Brinelin, the Moon Kraken

When Brinelin, the Moon Kraken enters and whenever you cast a spell with mana value 6 or greater, you may return target nonland permanent to its owner's hand.
Partner (You can have two commanders if both have partner.)

Neera, Wild Mage

Whenever you cast a spell, you may put it on the bottom of its owner's library. If you do, reveal cards from the top of your library until you reveal a nonland card. You may cast that card without paying its mana cost. Then put all revealed cards not cast this way on the bottom of your library in a random order. This ability triggers only once each turn.

Archmage Emeritus

Magecraft — Whenever you cast or copy an instant or sorcery spell, draw a card.