Consider

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

Marauding Brinefang

Ward {3} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {3}.)
Islandcycling {2} ({2}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

Guildsworn Prowler

Deathtouch
When Guildsworn Prowler dies, if it wasn't blocking, draw a card.

Mental Note

Elgaud Shieldmate

Soulbond (You may pair this creature with another unpaired creature when either enters. They remain paired for as long as you control both of them.)
As long as Elgaud Shieldmate is paired with another creature, both creatures have hexproof. (They can't be the targets of spells or abilities your opponents control.)

Whispersilk Cloak

Equipped creature can't be blocked and has shroud. (It can't be the target of spells or abilities.)
Equip {2}

Diregraf Horde

When Diregraf Horde enters, create two 2/2 black Zombie creature tokens with decayed. When you do, exile up to two target cards from graveyards. (A creature with decayed can't block. When it attacks, sacrifice it at end of combat.)

Burglar Rat

When this creature enters, each opponent discards a card.

Araumi of the Dead Tide

{T}, Exile cards from your graveyard equal to the number of opponents you have: Target creature card in your graveyard gains encore until end of turn. The encore cost is equal to its mana cost. (Exile the creature card and pay its mana cost: For each opponent, create a token copy that attacks that opponent this turn if able. They gain haste. Sacrifice them at the beginning of the next end step. Activate only as a sorcery.)

Street Wraith

Swampwalk (This creature can't be blocked as long as defending player controls a Swamp.)
Cycling—Pay 2 life. (Pay 2 life, Discard this card: Draw a card.)

Mind Stone

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

Elderfang Disciple

When Elderfang Disciple enters, each opponent discards a card.

Hidden Grotto

When Hidden Grotto enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
{T}: Add {C}.
{1}, {T}: Add one mana of any color.

Troll of Khazad-dûm

Troll of Khazad-dûm can't be blocked except by three or more creatures.
Swampcycling {1} ({1}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Thought Vessel

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

Sage's Row Denizen

Whenever another blue creature you control enters, target player mills two cards.

Desert of the Mindful

Desert of the Mindful enters tapped.
{T}: Add {U}.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)

Esper Panorama

{T}: Add {C}.
{1}, {T}, Sacrifice Esper Panorama: Search your library for a basic Plains, Island, or Swamp card, put it onto the battlefield tapped, then shuffle.

Kalastria Healer

Rally — Whenever Kalastria Healer or another Ally you control enters, each opponent loses 1 life and you gain 1 life.

Lonely Sandbar

Lonely Sandbar enters tapped.
{T}: Add {U}.
Cycling {U} ({U}, Discard this card: Draw a card.)

Refurbished Familiar

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Flying
When Refurbished Familiar enters, each opponent discards a card. For each opponent who can't, you draw a card.

Carrier Thrall

When Carrier Thrall dies, create a 1/1 colorless Eldrazi Scion creature token. It has "Sacrifice this creature: Add {C}."

Brainspoil

Destroy target creature that isn't enchanted. It can't be regenerated.
Transmute {1}{B}{B} ({1}{B}{B}, Discard this card: Search your library for a card with the same mana value as this card, reveal it, put it into your hand, then shuffle. Transmute only as a sorcery.)

Crow of Dark Tidings

Flying
When this creature enters or dies, mill two cards. (Put the top two cards of your library into your graveyard.)

Mindwrack Harpy

Flying
At the beginning of combat on your turn, each player mills three cards.

Archaeomancer

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

Vengeful Dead

Whenever Vengeful Dead or another Zombie dies, each opponent loses 1 life.

Obscura Storefront

When Obscura Storefront enters, sacrifice it. When you do, search your library for a basic Plains, Island, or Swamp card, put it onto the battlefield tapped, then shuffle and you gain 1 life.

Aethersnipe

When Aethersnipe enters, return target nonland permanent to its owner's hand.
Evoke {1}{U}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Abyssal Gatekeeper

When Abyssal Gatekeeper dies, each player sacrifices a creature of their choice.

Step Through

Return two target creatures to their owners' hands.
Wizardcycling {2} ({2}, Discard this card: Search your library for a Wizard card, reveal it, put it into your hand, then shuffle.)

Ransack the Lab

Look at the top three cards of your library. Put one of them into your hand and the rest into your graveyard.

Cloudkin Seer

Flying
When Cloudkin Seer enters, draw a card.

Mire Triton

Deathtouch
When Mire Triton enters, mill two cards and you gain 2 life. (To mill a card, put the top card of your library into your graveyard.)

Hisoka's Guard

You may choose not to untap Hisoka's Guard during your untap step.
{1}{U}, {T}: Target creature you control other than Hisoka's Guard has shroud for as long as Hisoka's Guard remains tapped. (It can't be the target of spells or abilities.)

Barren Moor

Barren Moor enters tapped.
{T}: Add {B}.
Cycling {B} ({B}, Discard this card: Draw a card.)

Swamp

Lotleth Giant

Undergrowth — When Lotleth Giant enters, it deals 1 damage to target opponent for each creature card in your graveyard.

Sky Diamond

Negate

Nimbleclaw Adept

Bigby's Hand — {T}: Untap two other target permanents. Activate only as a sorcery and only once each turn.

Dinrova Horror

When Dinrova Horror enters, return target permanent to its owner's hand, then that player discards a card.

Slum Reaper

When Slum Reaper enters, each player sacrifices a creature of their choice.

Gray Merchant of Asphodel

When Gray Merchant of Asphodel enters, each opponent loses X life, where X is your devotion to black. You gain life equal to the life lost this way. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Brotherhood Patriarch

When Brotherhood Patriarch dies, each opponent loses 2 life and you gain 2 life.

Strategic Planning

Dread Drone

When Dread Drone enters, create two 0/1 colorless Eldrazi Spawn creature tokens. They have "Sacrifice this creature: Add {C}."

Hieroglyphic Illumination

Draw two cards.
Cycling {U} ({U}, Discard this card: Draw a card.)

Stinkweed Imp

Flying
Whenever Stinkweed Imp deals combat damage to a creature, destroy that creature.
Dredge 5 (If you would draw a card, you may mill five cards instead. If you do, return this card from your graveyard to your hand.)

Careful Study

Drownyard Amalgam

When Drownyard Amalgam enters, target player mills three cards. (They put the top three cards of their library into their graveyard.)
{2}{U}: Drownyard Amalgam can't be blocked this turn.

Koilos Roc

Flash
Flying
When Koilos Roc enters, create a tapped Powerstone token. (It's an artifact with "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell.")

Mage's Guile

Target creature gains shroud until end of turn. (It can't be the target of spells or abilities.)
Cycling {U} ({U}, Discard this card: Draw a card.)

Ashen-Skin Zubera

When Ashen-Skin Zubera dies, target opponent discards a card for each Zubera that died this turn.

Teardrop Kami

Sacrifice Teardrop Kami: You may tap or untap target creature.

Moonlit Scavengers

When Moonlit Scavengers enters, if you control an artifact or enchantment, return target creature an opponent controls to its owner's hand.

Blight-Breath Catoblepas

When Blight-Breath Catoblepas enters, target creature an opponent controls gets -X/-X until end of turn, where X is your devotion to black. (Each {B} in the mana costs of permanents you control counts toward your devotion to black.)

Countervailing Winds

Counter target spell unless its controller pays {1} for each card in your graveyard.
Cycling {2} ({2}, Discard this card: Draw a card.)

Iceberg Cancrix

Whenever another snow permanent you control enters, you may have target player mill two cards.

Lórien Revealed

Draw three cards.
Islandcycling {1} ({1}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

Frantic Search

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

Command Tower

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

Stone Retrieval Unit

When Stone Retrieval Unit enters, create a tapped Powerstone token. (It's an artifact with "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell.")

Terramorphic Expanse

{T}, Sacrifice Terramorphic Expanse: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Suffocating Fumes

Creatures your opponents control get -1/-1 until end of turn.
Cycling {2} ({2}, Discard this card: Draw a card.)

Mirkwood Bats

Flying
Whenever you create or sacrifice a token, each opponent loses 1 life.

Polluted Mire

Polluted Mire enters tapped.
{T}: Add {B}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Prosperous Pirates

When Prosperous Pirates enters, create two Treasure tokens. (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Demon's Disciple

When Demon's Disciple enters, each player sacrifices a creature or planeswalker of their choice.

Perplex

Counter target spell unless its controller discards their hand.
Transmute {1}{U}{B} ({1}{U}{B}, Discard this card: Search your library for a card with the same mana value as this card, reveal it, put it into your hand, then shuffle. Transmute only as a sorcery.)

Projektor Inspector

Whenever Projektor Inspector or another Detective you control enters and whenever a Detective you control is turned face up, you may draw a card. If you do, discard a card.

Vizier of Tumbling Sands

{T}: Untap another target permanent.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)
When you cycle Vizier of Tumbling Sands, untap target permanent.

Elvish Doomsayer

When Elvish Doomsayer dies, each opponent discards a card.

Iceberg Titan

Whenever Iceberg Titan attacks, you may tap or untap target artifact or creature.

Inverted Iceberg

When Inverted Iceberg enters, mill a card, then draw a card. (To mill a card, put the top card of your library into your graveyard.)
Craft with artifact {4}{U}{U} ({4}{U}{U}, Exile this artifact, Exile another artifact you control or an artifact card from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.)

Inverted Iceberg // Iceberg Titan

Corridor Monitor

When Corridor Monitor enters, untap target artifact or creature you control.

Okiba-Gang Shinobi

Ninjutsu {3}{B} ({3}{B}, Return an unblocked attacker you control to hand: Put this card onto the battlefield from your hand tapped and attacking.)
Whenever Okiba-Gang Shinobi deals combat damage to a player, that player discards two cards.

Expunge

Destroy target nonartifact, nonblack creature. It can't be regenerated.
Cycling {2} ({2}, Discard this card: Draw a card.)

Filigree Familiar

When Filigree Familiar enters, you gain 2 life.
When Filigree Familiar dies, draw a card.

Necromancer's Assistant

When Necromancer's Assistant enters, mill three cards.

Tortured Existence

{B}, Discard a creature card: Return target creature card from your graveyard to your hand.

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.)

Curate

Surveil 2. (Look at the top two cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)
Draw a card.

Death's-Head Buzzard

Flying
When Death's-Head Buzzard dies, all creatures get -1/-1 until end of turn.

Skaab Goliath

As an additional cost to cast this spell, exile two creature cards from your graveyard.
Trample

Mulldrifter

Flying
When Mulldrifter enters, draw two cards.
Evoke {2}{U} (You may cast this spell for its evoke cost. If you do, it's sacrificed when it enters.)

Pestermite

Flash
Flying
When Pestermite enters, you may tap or untap target permanent.

Selhoff Occultist

Whenever Selhoff Occultist or another creature dies, target player mills a card.

Remote Isle

Remote Isle enters tapped.
{T}: Add {U}.
Cycling {2} ({2}, Discard this card: Draw a card.)

Thought Courier

Contingency Plan

Surveil 5. (Look at the top five cards of your library, then put any number of them into your graveyard and the rest on top of your library in any order.)

Morkrut Behemoth

As an additional cost to cast this spell, sacrifice a creature or pay {1}{B}.
Menace (This creature can't be blocked except by two or more creatures.)

Daggerfang Duo

Deathtouch
When Daggerfang Duo enters, you may mill two cards. (You may put the top two cards of your library into your graveyard.)

Loathsome Curator

Exploit (When this creature enters, you may sacrifice a creature.)
Menace
When Loathsome Curator exploits a creature, destroy target creature you don't control with mana value 3 or less.

Impaler Shrike

Flying
Whenever Impaler Shrike deals combat damage to a player, you may sacrifice it. If you do, draw three cards.

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice Commander's Sphere: Draw a card.

Wayfarer's Bauble

{2}, {T}, Sacrifice Wayfarer's Bauble: Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Grim Guardian

Constellation — Whenever Grim Guardian or another enchantment you control enters, each opponent loses 1 life.

Koma's Faithful

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
When Koma's Faithful dies, each player mills three cards. (They each put the top three cards of their library into their graveyard.)

Armored Skaab

When Armored Skaab enters, mill four cards.

Dimir Signet

Shardless Outlander

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Basic landcycling {2} ({2}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)

Fanatic of the Harrowing

When Fanatic of the Harrowing enters, each player discards a card. If you discarded a card this way, draw a card.

Charcoal Diamond

Charcoal Diamond enters tapped.
{T}: Add {B}.