Consider

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

Skyship Stalker

Flying
{R}: Skyship Stalker gets +1/+0 until end of turn.
{R}: Skyship Stalker gains first strike until end of turn.
{R}: Skyship Stalker gains haste until end of turn.

Pili-Pala

Flying
{2}, {Q}: Add one mana of any color. ({Q} is the untap symbol.)

Sulfurous Springs

{T}: Add {C}.
{T}: Add {B} or {R}. Sulfurous Springs deals 1 damage to you.

Blood Crypt

({T}: Add {B} or {R}.)
As Blood Crypt enters, you may pay 2 life. If you don't, it enters tapped.

Toxic Deluge

As an additional cost to cast this spell, pay X life.
All creatures get -X/-X until end of turn.

Arcane Denial

Counter target spell. Its controller may draw up to two cards at the beginning of the next turn's upkeep.
You draw a card at the beginning of the next turn's upkeep.

Morphic Pool

Morphic Pool enters tapped unless you have two or more opponents.
{T}: Add {U} or {B}.

Shivan Reef

{T}: Add {C}.
{T}: Add {U} or {R}. Shivan Reef deals 1 damage to you.

Thousand-Year Elixir

You may activate abilities of creatures you control as though those creatures had haste.
{1}, {T}: Untap target creature.

Candlekeep Sage

Commander creatures you own have "When this creature enters or leaves the battlefield, draw a card."

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Anger

Haste
As long as Anger is in your graveyard and you control a Mountain, creatures you control have haste.

Argent Sphinx

Flying
Metalcraft — {U}: Exile Argent Sphinx. Return it to the battlefield under your control at the beginning of the next end step. Activate only if you control three or more artifacts.

Dreamscape Artist

{2}{U}, {T}, Discard a card, Sacrifice a land: Search your library for up to two basic land cards, put them onto the battlefield, then shuffle.

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.")

Minion of Leshrac

Protection from black
At the beginning of your upkeep, Minion of Leshrac deals 5 damage to you unless you sacrifice a creature other than Minion of Leshrac. If Minion of Leshrac deals damage to you this way, tap it.
{T}: Destroy target creature or land.

The Deck of Many Things

{2}, {T}: Roll a d20 and subtract the number of cards in your hand. If the result is 0 or less, discard your hand.
1—9 | Return a card at random from your graveyard to your hand.
10—19 | Draw two cards.
20 | Put a creature card from any graveyard onto the battlefield under your control. When that creature dies, its owner loses the game.

Talisman of Creativity

{T}: Add {C}.
{T}: Add {U} or {R}. Talisman of Creativity deals 1 damage to you.

Exotic Orchard

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

Pendant of Prosperity

Pendant of Prosperity enters under the control of an opponent of your choice.
{2}, {T}: Draw a card, then you may put a land card from your hand onto the battlefield. Pendant of Prosperity's owner draws a card, then that player may put a land card from their hand onto the battlefield.

Training Grounds

Activated abilities of creatures you control cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Undercity Sewers

({T}: Add {U} or {B}.)
Undercity Sewers enters tapped.
When Undercity Sewers enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Rakdos Signet

Seat of the Synod

Cavern Harpy

Flying
When Cavern Harpy enters, return a blue or black creature you control to its owner's hand.
Pay 1 life: Return Cavern Harpy to its owner's hand.

Talisman of Indulgence

{T}: Add {C}.
{T}: Add {B} or {R}. Talisman of Indulgence deals 1 damage to you.

Staff of Domination

{1}: Untap Staff of Domination.
{2}, {T}: You gain 1 life.
{3}, {T}: Untap target creature.
{4}, {T}: Tap target creature.
{5}, {T}: Draw a card.

Bloodstained Mire

{T}, Pay 1 life, Sacrifice Bloodstained Mire: Search your library for a Swamp or Mountain card, put it onto the battlefield, then shuffle.

Heartstone

Activated abilities of creatures cost {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Steam Vents

({T}: Add {U} or {R}.)
As Steam Vents enters, you may pay 2 life. If you don't, it enters tapped.

Tree of Perdition

Defender
{T}: Exchange target opponent's life total with Tree of Perdition's toughness.

Azami, Lady of Scrolls

Tap an untapped Wizard you control: Draw a card.

Izzet Signet

Drowned Catacomb

Drowned Catacomb enters tapped unless you control an Island or a Swamp.
{T}: Add {U} or {B}.

Chaos Wand

{4}, {T}: Target opponent exiles cards from the top of their library until they exile an instant or sorcery card. You may cast that card without paying its mana cost. Then put the exiled cards that weren't cast this way on the bottom of that library in a random order.

Mountain

Spark Double

You may have Spark Double enter as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it's a creature, it enters with an additional loyalty counter on it if it's a planeswalker, and it isn't legendary.

Arcanis the Omnipotent

{T}: Draw three cards.
{2}{U}{U}: Return Arcanis to its owner's hand.

Patron of the Moon

Moonfolk offering (You may cast this spell any time you could cast an instant by sacrificing a Moonfolk and paying the difference in mana costs between this and the sacrificed Moonfolk. Mana cost includes color.)
Flying
{1}: Put up to two land cards from your hand onto the battlefield tapped.

Riptide Laboratory

{T}: Add {C}.
{1}{U}, {T}: Return target Wizard you control to its owner's hand.

Gamble

Search your library for a card, put that card into your hand, discard a card at random, then shuffle.

Aetherling

{U}: Exile Aetherling. Return it to the battlefield under its owner's control at the beginning of the next end step.
{U}: Aetherling can't be blocked this turn.
{1}: Aetherling gets +1/-1 until end of turn.
{1}: Aetherling gets -1/+1 until end of turn.

Swamp

Command Tower

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

Swan Song

Counter target enchantment, instant, or sorcery spell. Its controller creates a 2/2 blue Bird creature token with flying.

Feed the Swarm

Destroy target creature or enchantment an opponent controls. You lose life equal to that permanent's mana value.

Chainer, Nightmare Adept

Discard a card: You may cast a creature spell from your graveyard this turn. Activate only once each turn.
Whenever a nontoken creature you control enters, if you didn't cast it from your hand, it gains haste until your next turn.

Thundering Falls

({T}: Add {U} or {R}.)
Thundering Falls enters tapped.
When Thundering Falls enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Buried Alive

Search your library for up to three creature cards, put them into your graveyard, then shuffle.

Island

Reliquary Tower

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

Castle Vantress

Castle Vantress enters tapped unless you control an Island.
{T}: Add {U}.
{2}{U}{U}, {T}: Scry 2.

Mairsil, the Pretender

When Mairsil, the Pretender enters, you may exile an artifact or creature card from your hand or graveyard and put a cage counter on it.
Mairsil, the Pretender has all activated abilities of all cards you own in exile with cage counters on them. You may activate each of those abilities only once each turn.

Negate

Great Furnace

Urborg, Tomb of Yawgmoth

Each land is a Swamp in addition to its other land types.

Chainer, Dementia Master

All Nightmares get +1/+1.
{B}{B}{B}, Pay 3 life: Put target creature card from a graveyard onto the battlefield under your control. That creature is black and is a Nightmare in addition to its other creature types.
When Chainer, Dementia Master leaves the battlefield, exile all Nightmares.

Havengul Lich

{1}: You may cast target creature card in a graveyard this turn. When you cast it this turn, Havengul Lich gains all activated abilities of that card until end of turn.

Counterspell

Spikeshot Elder

{1}{R}{R}: Spikeshot Elder deals damage equal to its power to any target.

Asmodeus the Archfiend

Binding Contract — If you would draw a card, exile the top card of your library face down instead.
{B}{B}{B}: Draw seven cards.
{B}: Return all cards exiled with Asmodeus the Archfiend to their owner's hand and you lose that much life.

Talisman of Dominance

{T}: Add {C}.
{T}: Add {U} or {B}. Talisman of Dominance deals 1 damage to you.

Prismatic Vista

{T}, Pay 1 life, Sacrifice Prismatic Vista: Search your library for a basic land card, put it onto the battlefield, then shuffle.

Panharmonicon

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

Thassa, Deep-Dwelling

Indestructible
As long as your devotion to blue is less than five, Thassa isn't a creature.
At the beginning of your end step, exile up to one other target creature you control, then return that card to the battlefield under your control.
{3}{U}: Tap another target creature.

Underground River

{T}: Add {C}.
{T}: Add {U} or {B}. Underground River deals 1 damage to you.

Essence Flux

Exile target creature you control, then return that card to the battlefield under its owner's control. If it's a Spirit, put a +1/+1 counter on it.

Illusionist's Bracers

Whenever an ability of equipped creature is activated, if it isn't a mana ability, copy that ability. You may choose new targets for the copy.
Equip {3}

Blasphemous Act

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

Surge Engine

Defender
{U}: Surge Engine loses defender and gains "This creature can't be blocked."
{2}{U}: Surge Engine becomes blue and has base power and toughness 5/4. Activate only if Surge Engine doesn't have defender.
{4}{U}{U}: Draw three cards. Activate only if Surge Engine is blue and only once.

Otawara, Soaring City

{T}: Add {U}.
Channel — {3}{U}, Discard Otawara, Soaring City: Return target artifact, creature, enchantment, or planeswalker to its owner's hand. This ability costs {1} less to activate for each legendary creature you control.

Coveted Jewel

When Coveted Jewel enters, draw three cards.
{T}: Add three mana of any one color.
Whenever one or more creatures an opponent controls attack you and aren't blocked, that player draws three cards and gains control of Coveted Jewel. Untap it.

Torchling

{R}: Untap Torchling.
{R}: Target creature blocks Torchling this turn if able.
{R}: Change the target of target spell that targets only Torchling.
{1}: Torchling gets +1/-1 until end of turn.
{1}: Torchling gets -1/+1 until end of turn.

Gilded Lotus

Mirror-Mad Phantasm

Flying
{1}{U}: Mirror-Mad Phantasm's owner shuffles it into their library. If that player does, they reveal cards from the top of that library until a card named Mirror-Mad Phantasm is revealed. The player puts that card onto the battlefield and all other cards revealed this way into their graveyard.

Feldon of the Third Path

{2}{R}, {T}: Create a token that's a copy of target creature card in your graveyard, except it's an artifact in addition to its other types. It gains haste. Sacrifice it at the beginning of the next end step.

Endling

{B}: Endling gains menace until end of turn.
{B}: Endling gains deathtouch until end of turn.
{B}: Endling gains undying until end of turn. (When this creature 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.)
{1}: Endling gets +1/-1 or -1/+1 until end of turn.

Dimir Signet

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.)

Quicksilver Elemental

{U}: Quicksilver Elemental gains all activated abilities of target creature until end of turn. (If any of the abilities use that creature's name, use this creature's name instead.)
You may spend blue mana as though it were mana of any color to pay the activation costs of Quicksilver Elemental's abilities.

Arcane Signet

Sol Ring

Jace's Archivist

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

Frantic Search

Draw two cards, then discard two cards. Untap up to three lands.

Watery Grave

({T}: Add {U} or {B}.)
As Watery Grave enters, you may pay 2 life. If you don't, it enters tapped.

Scalding Tarn

{T}, Pay 1 life, Sacrifice Scalding Tarn: Search your library for an Island or Mountain card, put it onto the battlefield, then shuffle.

Rakdos Charm

Choose one —
• Exile target player's graveyard.
• Destroy target artifact.
• Each creature deals 1 damage to its controller.

Irenicus's Vile Duplication

Create a token that's a copy of target creature you control, except the token has flying and it isn't legendary.

Training Center

Training Center enters tapped unless you have two or more opponents.
{T}: Add {U} or {R}.

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.

Collector's Vault

{2}, {T}: Draw a card, then discard a card. Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Mirage Mirror

{2}: Mirage Mirror becomes a copy of target artifact, creature, enchantment, or land until end of turn.

Thought Scour

Target player mills two cards.
Draw a card.

Ghostly Flicker

Exile two target artifacts, creatures, and/or lands you control, then return those cards to the battlefield under your control.

Raucous Theater

({T}: Add {B} or {R}.)
Raucous Theater enters tapped.
When Raucous Theater enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Sulfur Falls

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

Pack Rat

Pack Rat's power and toughness are each equal to the number of Rats you control.
{2}{B}, Discard a card: Create a token that's a copy of Pack Rat.

Conjurer's Closet

At the beginning of your end step, you may exile target creature you control, then return that card to the battlefield under your control.