Capricopian

Capricopian enters with X +1/+1 counters on it.
{2}: Put a +1/+1 counter on Capricopian, then you may reselect which player Capricopian is attacking. Only the player Capricopian is attacking may activate this ability and only during the declare attackers step. (It can't attack its controller.)

Agent of Treachery

When Agent of Treachery enters, gain control of target permanent.
At the beginning of your end step, if you control three or more permanents you don't own, draw three cards.

Craterhoof Behemoth

Haste
When Craterhoof Behemoth enters, creatures you control gain trample and get +X/+X until end of turn, where X is the number of creatures you control.

Conclave Naturalists

When Conclave Naturalists enters, you may destroy target artifact or enchantment.

Frilled Mystic

Flash
When Frilled Mystic enters, you may counter target spell.

Cloud of Faeries

Flying
When Cloud of Faeries enters, untap up to two lands.
Cycling {2} ({2}, Discard this card: Draw a card.)

Quandrix Cultivator

When Quandrix Cultivator enters, you may search your library for a basic Forest or Island card, put it onto the battlefield, then shuffle.

District Guide

When District Guide enters, you may search your library for a basic land card or Gate card, reveal it, put it into your hand, then shuffle.

Mizzium Meddler

Flash (You may cast this spell any time you could cast an instant.)
When Mizzium Meddler enters, you may change a target of target spell or ability to Mizzium Meddler.

Hydroid Krasis

When you cast this spell, you gain half X life and draw half X cards. Round down each time.
Flying, trample
Hydroid Krasis enters with X +1/+1 counters on it.

Arborback Stomper

Trample
When Arborback Stomper enters, you gain 5 life.

Aether Channeler

When Aether Channeler enters, choose one —
• Create a 1/1 white Bird creature token with flying.
• Return another target nonland permanent to its owner's hand.
• Draw a card.

Marshdrinker Giant

When Marshdrinker Giant enters, destroy target Island or Swamp an opponent controls.

Hornet Queen

Flying, deathtouch
When Hornet Queen enters, create four 1/1 green Insect creature tokens with flying and deathtouch.

Bond Beetle

When Bond Beetle enters, put a +1/+1 counter on target creature.

Jace's Mindseeker

Flying
When Jace's Mindseeker enters, target opponent mills five cards. You may cast an instant or sorcery spell from among them without paying its mana cost.

Rishadan Cutpurse

When Rishadan Cutpurse enters, each opponent sacrifices a permanent unless they pay {1}.

Master Biomancer

Each other creature you control enters with a number of additional +1/+1 counters on it equal to Master Biomancer's power and as a Mutant in addition to its other types.

Endurance

Flash
Reach
When Endurance enters, up to one target player puts all the cards from their graveyard on the bottom of their library in a random order.
Evoke—Exile a green card from your hand.

Diluvian Primordial

Flying
When Diluvian Primordial enters, for each opponent, you may cast up to one target instant or sorcery card from that player's graveyard without paying its mana cost. If a spell cast this way would be put into a graveyard, exile it instead.

Coiling Oracle

When Coiling Oracle enters, reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put that card into your hand.

Manglehorn

When Manglehorn enters, you may destroy target artifact.
Artifacts your opponents control enter tapped.

Peregrine Drake

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

Deadeye Navigator

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 Deadeye Navigator is paired with another creature, each of those creatures has "{1}{U}: Exile this creature, then return it to the battlefield under your control."

Avenger of Zendikar

When Avenger of Zendikar enters, create a 0/1 green Plant creature token for each land you control.
Landfall — Whenever a land you control enters, you may put a +1/+1 counter on each Plant creature you control.

Eternal Witness

When Eternal Witness enters, you may return target card from your graveyard to your hand.

Mystic Snake

Flash
When Mystic Snake enters, counter target spell.

Reclamation Sage

When Reclamation Sage enters, you may destroy target artifact or enchantment.

Nissa, Sage Animist

+1: Reveal the top card of your library. If it's a land card, put it onto the battlefield. Otherwise, put it into your hand.
−2: Create Ashaya, the Awoken World, a legendary 4/4 green Elemental creature token.
−7: Untap up to six target lands. They become 6/6 Elemental creatures. They're still lands.

Nissa, Vastwood Seer

When Nissa, Vastwood Seer enters, you may search your library for a basic Forest card, reveal it, put it into your hand, then shuffle.
Whenever a land you control enters, if you control seven or more lands, exile Nissa, then return her to the battlefield transformed under her owner's control.

Nissa, Vastwood Seer // Nissa, Sage Animist

Deceiver Exarch

Flash (You may cast this spell any time you could cast an instant.)
When Deceiver Exarch enters, choose one —
• Untap target permanent you control.
• Tap target permanent an opponent controls.

Breaching Hippocamp

Flash (You may cast this spell any time you could cast an instant.)
When Breaching Hippocamp enters, untap another target creature you control.

Manifestation Sage

When Manifestation Sage enters, create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it, where X is the number of cards in your hand.

Prime Speaker Zegana

Prime Speaker Zegana enters with X +1/+1 counters on it, where X is the greatest power among other creatures you control.
When Prime Speaker Zegana enters, draw cards equal to its power.

Fierce Empath

When Fierce Empath enters, you may search your library for a creature card with mana value 6 or greater, reveal it, put it into your hand, then shuffle.

Hyrax Tower Scout

When Hyrax Tower Scout enters, untap target creature.

Circuit Mender

When Circuit Mender enters, you gain 2 life.
When Circuit Mender leaves the battlefield, draw a card.

Merfolk Skydiver

Flying
When Merfolk Skydiver enters, put a +1/+1 counter on target creature you control.
{3}{G}{U}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Corridor Monitor

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

Bounding Krasis

Flash (You may cast this spell any time you could cast an instant.)
When Bounding Krasis enters, you may tap or untap target creature.

Acidic Slime

Deathtouch (Any amount of damage this deals to a creature is enough to destroy it.)
When Acidic Slime enters, destroy target artifact, enchantment, or land.

Deepglow Skate

When Deepglow Skate enters, double the number of each kind of counter on any number of target permanents.

Marwyn, the Nurturer

Whenever another Elf you control enters, put a +1/+1 counter on Marwyn, the Nurturer.
{T}: Add an amount of {G} equal to Marwyn's power.

Keeper of Keys

When Keeper of Keys enters, you become the monarch.
At the beginning of your upkeep, if you're the monarch, creatures you control can't be blocked this turn.

Greenwarden of Murasa

When Greenwarden of Murasa enters, you may return target card from your graveyard to your hand.
When Greenwarden of Murasa dies, you may exile it. If you do, return target card from your graveyard to your hand.

Carven Caryatid

Defender (This creature can't attack.)
When Carven Caryatid enters, draw a card.

Heroes' Bane

Heroes' Bane enters with four +1/+1 counters on it.
{2}{G}{G}: Put X +1/+1 counters on Heroes' Bane, where X is its power.

Elvish Visionary

When Elvish Visionary enters, draw a card.

Armorcraft Judge

When Armorcraft Judge enters, draw a card for each creature you control with a +1/+1 counter on it.

Archaeomancer

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

Pelt Collector

Whenever another creature you control enters or dies, if that creature's power is greater than Pelt Collector's, put a +1/+1 counter on Pelt Collector.
As long as Pelt Collector has three or more +1/+1 counters on it, it has trample.