Season of Growth

Whenever a creature you control enters, scry 1. (Look at the top card of your library. You may put that card on the bottom.)
Whenever you cast a spell that targets a creature you control, draw a card.

Stormrider Rig

Equipped creature gets +1/+1.
Whenever a creature you control enters, you may attach this Equipment to it.
Equip {2}

Battering Krasis

Trample
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Bloodstained Mire

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

Wild Pair

Whenever a creature enters, if you cast it from your hand, you may search your library for a creature card with the same total power and toughness, put it onto the battlefield, then shuffle.

Verdant Catacombs

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

Healer of the Pride

Whenever another creature you control enters, you gain 2 life.

Mace of the Valiant

Equipped creature gets +1/+1 for each charge counter on this Equipment and has vigilance. (Attacking doesn't cause it to tap.)
Whenever a creature you control enters, put a charge counter on this Equipment.
Equip {3}

Kruin Striker

Whenever another creature you control enters, this creature gets +1/+0 and gains trample until end of turn. (It can deal excess combat damage to the player or planeswalker it's attacking.)

Marsh Flats

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

Call

Create four 1/1 white Bird creature tokens with flying.
Fuse (You may cast one or both halves of this card from your hand.)

Beck

Whenever a creature enters this turn, you may draw a card.
Fuse (You may cast one or both halves of this card from your hand.)

Beck // Call

Savannah

Wretched Anurid

Whenever another creature enters, you lose 1 life.

Rampaging Ferocidon

Menace
Players can't gain life.
Whenever another creature enters, this creature deals 1 damage to that creature's controller.

Taiga

Blasting Station

{T}, Sacrifice a creature: This artifact deals 1 damage to any target.
Whenever a creature enters, you may untap this artifact.

Tundra

Impact Tremors

Whenever a creature you control enters, this enchantment deals 1 damage to each opponent.

Portcullis

Whenever a creature enters, if there are two or more other creatures on the battlefield, exile that creature. Return that card to the battlefield under its owner's control when this artifact leaves the battlefield.

Goldnight Commander

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

Simic Manipulator

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
{T}, Remove one or more +1/+1 counters from this creature: Gain control of target creature with power less than or equal to the number of +1/+1 counters removed this way.

Illusory Gains

Enchant creature
You control enchanted creature.
Whenever a creature an opponent controls enters, attach this Aura to that creature.

Lukka, Wayward Bonder

+1: You may discard a card. If you do, draw a card. If a creature card was discarded this way, draw two cards instead.
−2: Return target creature card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of your next upkeep.
−7: You get an emblem with "Whenever a creature you control enters, it deals damage equal to its power to any target."

Mila, Crafty Companion

Whenever an opponent attacks one or more planeswalkers you control, put a loyalty counter on each planeswalker you control.
Whenever a permanent you control becomes the target of a spell or ability an opponent controls, you may draw a card.

Mila, Crafty Companion // Lukka, Wayward Bonder

Leyline of Vitality

If this card is in your opening hand, you may begin the game with it on the battlefield.
Creatures you control get +0/+1.
Whenever a creature you control enters, you may gain 1 life.

Godless Shrine

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

Primal Forcemage

Whenever another creature you control enters, that creature gets +3/+3 until end of turn.

Authority of the Consuls

Creatures your opponents control enter tapped.
Whenever a creature an opponent controls enters, you gain 1 life.

Mana Confluence

{T}, Pay 1 life: Add one mana of any color.

Ogre Battledriver

Whenever another creature you control enters, that creature gets +2/+0 and gains haste until end of turn. (It can attack and {T} this turn.)

Path of Discovery

Whenever a creature you control enters, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on the creature, then put the card back or put it into your graveyard.)

Herd Gnarr

Whenever another creature you control enters, this creature gets +2/+2 until end of turn.

Sunstrike Legionnaire

This creature doesn't untap during your untap step.
Whenever another creature enters, untap this creature.
{T}: Tap target creature with mana value 3 or less.

Wooded Foothills

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

Griffin Protector

Flying
Whenever another creature you control enters, this creature gets +1/+1 until end of turn.

Durable Handicraft

Whenever a creature you control enters, you may pay {1}. If you do, put a +1/+1 counter on that creature.
{5}{G}, Sacrifice this enchantment: Put a +1/+1 counter on each creature you control.

Scurry Oak

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Whenever one or more +1/+1 counters are put on this creature, you may create a 1/1 green Squirrel creature token.

Crocanura

Reach (This creature can block creatures with flying.)
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Unstable Shapeshifter

Whenever another creature enters, this creature becomes a copy of that creature, except it has this ability.

Olivia, Mobilized for War

Flying
Whenever another creature you control enters, you may discard a card. If you do, put a +1/+1 counter on that creature, it gains haste until end of turn, and it becomes a Vampire in addition to its other types.

Boltwing Marauder

Flying
Whenever another creature you control enters, target creature gets +2/+0 until end of turn.

Ronin Warclub

Equipped creature gets +2/+1.
Whenever a creature you control enters, attach this Equipment to that creature.
Equip {5} ({5}: Attach to target creature you control. Equip only as a sorcery.)

Volcanic Island

Selvala, Heart of the Wilds

Whenever another creature enters, its controller may draw a card if its power is greater than each other creature's power.
{G}, {T}: Add X mana in any combination of colors, where X is the greatest power among creatures you control.

Gluttonous Slug

Menace
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Huatli, Radiant Champion

+1: Put a loyalty counter on Huatli for each creature you control.
−1: Target creature gets +X/+X until end of turn, where X is the number of creatures you control.
−8: You get an emblem with "Whenever a creature you control enters, you may draw a card."

Aether Flash

Whenever a creature enters, this enchantment deals 2 damage to it.

Novijen Sages

Graft 4 (This creature enters with four +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{1}, Remove two +1/+1 counters from among creatures you control: Draw a card.

Emiel the Blessed

{3}: Exile another target creature you control, then return it to the battlefield under its owner's control.
Whenever another creature you control enters, you may pay {G/W}. If you do, put a +1/+1 counter on it. If it's a Unicorn, put two +1/+1 counters on it instead. ({G/W} can be paid with either {G} or {W}.)

Llanowar Reborn

This land enters tapped.
{T}: Add {G}.
Graft 1 (This land enters with a +1/+1 counter on it. Whenever a creature enters, you may move a +1/+1 counter from this land onto it.)

Pandemonium

Whenever a creature enters, that creature's controller may have it deal damage equal to its power to any target of their choice.

Bronzebeak Moa

Whenever another creature you control enters, this creature gets +3/+3 until end of turn.

Overgrown Tomb

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

Intruder Alarm

Creatures don't untap during their controllers' untap steps.
Whenever a creature enters, untap all creatures.

In the Web of War

Whenever a creature you control enters, it gets +2/+0 and gains haste until end of turn.

Valor in Akros

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

Gyre Sage

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
{T}: Add {G} for each +1/+1 counter on this creature.

Command Tower

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

Underground Sea

Cytospawn Shambler

Graft 6 (This creature enters with six +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{G}: Target creature with a +1/+1 counter on it gains trample until end of turn.

Prison Term

Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated.
Whenever a creature an opponent controls enters, you may attach this Aura to that creature.

Saltskitter

Whenever another creature enters, exile this creature. Return this creature to the battlefield under its owner's control at the beginning of the next end step.

Aura Shards

Whenever a creature you control enters, you may destroy target artifact or enchantment.

Experiment One

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Remove two +1/+1 counters from this creature: Regenerate it. (The next time this creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Bayou

Juniper Order Ranger

Whenever another creature you control enters, put a +1/+1 counter on that creature and a +1/+1 counter on this creature.

Tropical Island

Sai of the Shinobi

Shielded by Faith

Enchant creature
Enchanted creature has indestructible.
Whenever a creature enters, you may attach this Aura to that creature.

Temple Garden

({T}: Add {G} or {W}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Sacred Foundry

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

Simic Fluxmage

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
{1}{U}, {T}: Move a +1/+1 counter from this creature onto target creature.

Windswept Heath

{T}, Pay 1 life, Sacrifice this land: Search your library for a Forest or Plains card, put it onto the battlefield, then shuffle.

Aquastrand Spider

Graft 2 (This creature enters with two +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{G}: Target creature with a +1/+1 counter on it gains reach until end of turn. (It can block creatures with flying.)

Blood Crypt

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

Plaxcaster Frogling

Graft 3 (This creature enters with three +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{2}: Target creature with a +1/+1 counter on it gains shroud until end of turn. (It can't be the target of spells or abilities.)

Prized Amalgam

Whenever a creature enters, if it entered from your graveyard or you cast it from your graveyard, return this card from your graveyard to the battlefield tapped at the beginning of the next end step.

Polluted Delta

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

Indatha Triome

({T}: Add {W}, {B}, or {G}.)
This land enters tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

Hamletback Goliath

Whenever another creature enters, you may put X +1/+1 counters on this creature, where X is that creature's power.

Terror of the Peaks

Flying
Spells your opponents cast that target this creature cost an additional 3 life to cast.
Whenever another creature you control enters, this creature deals damage equal to that creature's power to any target.

Mana Echoes

Whenever a creature enters, you may add an amount of {C} equal to the number of creatures you control that share a creature type with it.

Misty Rainforest

{T}, Pay 1 life, Sacrifice this land: Search your library for a Forest or Island card, put it onto the battlefield, then shuffle.

Soultether Golem

Vanishing 1 (This creature enters with a time counter on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
Whenever another creature you control enters, put a time counter on this creature.

Carnival of Souls

Whenever a creature enters, you lose 1 life and add {B}.

Death Match

Whenever a creature enters, that creature's controller may have target creature of their choice get -3/-3 until end of turn.

Helium Squirter

Graft 3 (This creature enters with three +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{1}: Target creature with a +1/+1 counter on it gains flying until end of turn.

Emcee

Whenever another creature enters, you may stand up and say in a deep, booming voice, "Presenting . . . " and that creature's name. If you do, put a +1/+1 counter on that creature.

Flooded Strand

{T}, Pay 1 life, Sacrifice this land: Search your library for a Plains or Island card, put it onto the battlefield, then shuffle.

Stomping Ground

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

Essence Warden

Whenever another creature enters, you gain 1 life.

Prosperous Innkeeper

When this creature enters, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Whenever another creature you control enters, you gain 1 life.

Cytoplast Manipulator

Graft 2 (This creature enters with two +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{U}, {T}: Gain control of target creature with a +1/+1 counter on it for as long as this creature remains on the battlefield.

Sporeback Troll

Graft 2 (This creature enters with two +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
{1}{G}: Regenerate target creature with a +1/+1 counter on it.

Warstorm Surge

Whenever a creature you control enters, it deals damage equal to its power to any target.

Poisonbelly Ogre

Whenever another creature enters, its controller loses 1 life.

Nurturing Presence

Enchant creature
Enchanted creature has "Whenever a creature you control enters, this creature gets +1/+1 until end of turn."
When this Aura enters, create a 1/1 white Spirit creature token with flying.

Decoction Module

Whenever a creature you control enters, you get {E} (an energy counter).
{4}, {T}: Return target creature you control to its owner's hand.

Simic Initiate

Graft 1 (This creature enters with a +1/+1 counter on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)

Badlands

First Day of Class

Whenever a creature you control enters this turn, put a +1/+1 counter on it and it gains haste until end of turn.
Learn. (You may reveal a Lesson card you own from outside the game and put it into your hand, or discard a card to draw a card.)

Soul's Attendant

Whenever another creature enters, you may gain 1 life.

Luminous Phantom

Flying
Whenever another creature you control leaves the battlefield, you gain 1 life.
If Luminous Phantom would be put into a graveyard from anywhere, exile it instead.