Valor in Akros

Whenever a creature you control enters, creatures you control get +1/+1 until end of turn.

Selfless Spirit

Flying
Sacrifice Selfless Spirit: Creatures you control gain indestructible until end of turn.

Ugin's Conjurant

Ugin's Conjurant enters with X +1/+1 counters on it.
If damage would be dealt to Ugin's Conjurant while it has a +1/+1 counter on it, prevent that damage and remove that many +1/+1 counters from Ugin's Conjurant.

Rootborn Defenses

Populate. Creatures you control gain indestructible until end of turn. (To populate, create a token that's a copy of a creature token you control.)

Soul Warden

Whenever another creature enters, you gain 1 life.

Subjugator Angel

Flying
When Subjugator Angel enters, tap all creatures your opponents control.

Mardu Woe-Reaper

Whenever Mardu Woe-Reaper or another Warrior you control enters, you may exile target creature card from a graveyard. If you do, you gain 1 life.

Hedron Archive

{T}: Add {C}{C}.
{2}, {T}, Sacrifice this artifact: Draw two cards.

Conclave Phalanx

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
When Conclave Phalanx enters, you gain 1 life for each creature you control.

Marble Diamond

Marble Diamond enters tapped.
{T}: Add {W}.

Gold Myr

Oketra's Monument

White creature spells you cast cost {1} less to cast.
Whenever you cast a creature spell, create a 1/1 white Warrior creature token with vigilance.

Stonecloaker

Flash
Flying
When Stonecloaker enters, return a creature you control to its owner's hand.
When Stonecloaker enters, exile target card from a graveyard.

Dauntless Bodyguard

As Dauntless Bodyguard enters, choose another creature you control.
Sacrifice Dauntless Bodyguard: The chosen creature gains indestructible until end of turn.

Aviary Mechanic

When Aviary Mechanic enters, you may return another permanent you control to its owner's hand.

Martyred Rusalka

{W}, Sacrifice a creature: Target creature can't attack this turn.

Kor Skyfisher

Flying
When Kor Skyfisher enters, return a permanent you control to its owner's hand.

Plains

Millikin

{T}, Mill a card: Add {C}. (To mill a card, put the top card of your library into your graveyard.)

War Priest of Thune

When War Priest of Thune enters, you may destroy target enchantment.

Endless One

Endless One enters with X +1/+1 counters on it.

Jeskai Barricade

Flash (You may cast this spell any time you could cast an instant.)
Defender
When Jeskai Barricade enters, you may return another target creature you control to its owner's hand.

Mentor of the Meek

Whenever another creature you control with power 2 or less enters, you may pay {1}. If you do, draw a card.

Skyscanner

Flying
When Skyscanner enters, draw a card.

Make a Stand

Creatures you control get +1/+0 and gain indestructible until end of turn. (Damage and effects that say "destroy" don't destroy them.)

Children of Korlis

Sacrifice Children of Korlis: You gain life equal to the life you've lost this turn. (Damage causes loss of life.)

Ornithopter

Akroma's Blessing

Choose a color. Creatures you control gain protection from the chosen color until end of turn.
Cycling {W} ({W}, Discard this card: Draw a card.)

Eiganjo Free-Riders

Flying
At the beginning of your upkeep, return a white creature you control to its owner's hand.

Emancipation Angel

Flying
When Emancipation Angel enters, return a permanent you control to its owner's hand.

Thraben Inspector

When Thraben Inspector enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Palladium Myr

Bygone Bishop

Flying
Whenever you cast a creature spell with mana value 3 or less, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Umbilicus

At the beginning of each player's upkeep, that player may pay 2 life. If they don't, they return a permanent they control to its owner's hand.

Dust Elemental

Flash (You may cast this spell any time you could cast an instant.)
Flying; fear (This creature can't be blocked except by artifact creatures and/or black creatures.)
When Dust Elemental enters, return three creatures you control to their owner's hand.

Benalish Marshal

Imposing Sovereign

Creatures your opponents control enter tapped.

Scapegoat

As an additional cost to cast this spell, sacrifice a creature.
Return any number of target creatures you control to their owner's hand.

Leonin Relic-Warder

When Leonin Relic-Warder enters, you may exile target artifact or enchantment.
When Leonin Relic-Warder leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Kami of False Hope

Sacrifice Kami of False Hope: Prevent all combat damage that would be dealt this turn.

Hedron Crawler

{T}: Add {C}. ({C} represents colorless mana.)

Loyal Sentry

When Loyal Sentry blocks a creature, destroy that creature and Loyal Sentry.

Reverent Mantra

You may exile a white card from your hand rather than pay this spell's mana cost.
Choose a color. All creatures gain protection from the chosen color until end of turn.

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.

Infiltration Lens

Whenever equipped creature becomes blocked by a creature, you may draw two cards.
Equip {1}

Oblation

The owner of target nonland permanent shuffles it into their library, then draws two cards.

Phyrexian Walker

Whitemane Lion

Flash
When Whitemane Lion enters, return a creature you control to its owner's hand.

Venerated Loxodon

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
When Venerated Loxodon enters, put a +1/+1 counter on each creature that convoked it.

Signal Pest

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
Signal Pest can't be blocked except by creatures with flying or reach.

Binding Mummy

Whenever another Zombie you control enters, you may tap target artifact or creature.

God-Eternal Oketra

Double strike
Whenever you cast a creature spell, create a 4/4 black Zombie Warrior creature token with vigilance.
When God-Eternal Oketra dies or is put into exile from the battlefield, you may put it into its owner's library third from the top.

Wall of Omens

Defender
When Wall of Omens enters, draw a card.

Shifting Wall

Defender (This creature can't attack.)
Shifting Wall enters with X +1/+1 counters on it.

Ancestral Statue

When Ancestral Statue enters, return a nonland permanent you control to its owner's hand.

Benevolent Bodyguard

Sacrifice Benevolent Bodyguard: Target creature you control gains protection from the color of your choice until end of turn.

Stormfront Riders

Flying
When Stormfront Riders enters, return two creatures you control to their owner's hand.
Whenever Stormfront Riders or another creature is returned to your hand from the battlefield, create a 1/1 white Soldier creature token.

Blood Clock

At the beginning of each player's upkeep, that player returns a permanent they control to its owner's hand unless they pay 2 life.

Angelic Chorus

Whenever a creature you control enters, you gain life equal to its toughness.

Victory's Herald

Flying
Whenever Victory's Herald attacks, attacking creatures gain flying and lifelink until end of turn.

Resolute Watchdog

Defender
{1}, Sacrifice Resolute Watchdog: Target creature you control gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Mind Stone

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

Alms Collector

Flash
If an opponent would draw two or more cards, instead you and that player each draw a card.

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.