Territorial Scythecat

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Landfall — Whenever a land you control enters, put a +1/+1 counter on Territorial Scythecat.

Forerunner of the Heralds

When Forerunner of the Heralds enters, you may search your library for a Merfolk card, reveal it, then shuffle and put that card on top.
Whenever another Merfolk you control enters, put a +1/+1 counter on Forerunner of the Heralds.

Oneirophage

Flying
Whenever you draw a card, put a +1/+1 counter on Oneirophage.

Forced Adaptation

Enchant creature
At the beginning of your upkeep, put a +1/+1 counter on enchanted creature.

Woodland Champion

Whenever one or more tokens you control enter, put that many +1/+1 counters on Woodland Champion.

Primal Cocoon

Enchant creature
At the beginning of your upkeep, put a +1/+1 counter on enchanted creature.
When enchanted creature attacks or blocks, sacrifice Primal Cocoon.

Go-Shintai of Boundless Vigor

Trample
At the beginning of your end step, you may pay {1}. When you do, put a +1/+1 counter on target Shrine for each Shrine you control.

Invigorating Surge

Put a +1/+1 counter on target creature you control, then double the number of +1/+1 counters on that creature.

Nadir Kraken

Whenever you draw a card, you may pay {1}. If you do, put a +1/+1 counter on Nadir Kraken and create a 1/1 blue Tentacle creature token.

Jace's Projection

Whenever you draw a card, put a +1/+1 counter on Jace's Projection.
{3}{U}: Put a loyalty counter on target Jace planeswalker.

Simic Ascendancy

{1}{G}{U}: Put a +1/+1 counter on target creature you control.
Whenever one or more +1/+1 counters are put on a creature you control, put that many growth counters on Simic Ascendancy.
At the beginning of your upkeep, if Simic Ascendancy has twenty or more growth counters on it, you win the game.

Fairgrounds Trumpeter

At the beginning of each end step, if a +1/+1 counter was put on a permanent under your control this turn, put a +1/+1 counter on Fairgrounds Trumpeter.

Packsong Pup

At the beginning of combat on your turn, if you control another Wolf or Werewolf, put a +1/+1 counter on Packsong Pup.
When Packsong Pup dies, you gain life equal to its power.

Contortionist Troupe

Contortionist Troupe enters with X +1/+1 counters on it.
Coven — At the beginning of your end step, if you control three or more creatures with different powers, put a +1/+1 counter on target creature you control.

Forest

Lorescale Coatl

Whenever you draw a card, put a +1/+1 counter on Lorescale Coatl.

Vastwood Thicket

Vastwood Thicket enters tapped.
{T}: Add {G}.

Vastwood Fortification

Vastwood Fortification // Vastwood Thicket

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.

Titania's Chosen

Whenever a player casts a green spell, put a +1/+1 counter on Titania's Chosen.

Lumberknot

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Whenever a creature dies, put a +1/+1 counter on Lumberknot.

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 Experiment One: Regenerate Experiment One. (The next time this creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Vinelasher Kudzu

Landfall — Whenever a land you control enters, put a +1/+1 counter on Vinelasher Kudzu.

Managorger Hydra

Trample
Whenever a player casts a spell, put a +1/+1 counter on Managorger Hydra.

Courage in Crisis

Put a +1/+1 counter on target creature, then proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)

Combine Guildmage

{1}{G}, {T}: This turn, each creature you control enters with an additional +1/+1 counter on it.
{1}{U}, {T}: Move a +1/+1 counter from target creature you control onto another target creature you control.

Quandrix Pledgemage

Magecraft — Whenever you cast or copy an instant or sorcery spell, put a +1/+1 counter on Quandrix Pledgemage.

Hydra's Growth

Enchant creature
When Hydra's Growth enters, put a +1/+1 counter on enchanted creature.
At the beginning of your upkeep, double the number of +1/+1 counters on enchanted creature.

Gobbling Ooze

{G}, Sacrifice another creature: Put a +1/+1 counter on Gobbling Ooze.

Solidarity of Heroes

Strive — This spell costs {1}{G} more to cast for each target beyond the first.
Choose any number of target creatures. Double the number of +1/+1 counters on each of them.

Hall of Oracles

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
{T}: Put a +1/+1 counter on target creature. Activate only as a sorcery and only if you've cast an instant or sorcery spell this turn.

Biogenic Ooze

When Biogenic Ooze enters, create a 2/2 green Ooze creature token.
At the beginning of your end step, put a +1/+1 counter on each Ooze you control.
{1}{G}{G}{G}: Create a 2/2 green Ooze creature token.

Ring of Kalonia

Equipped creature has trample. (It can deal excess combat damage to the player or planeswalker it's attacking.)
At the beginning of your upkeep, put a +1/+1 counter on equipped creature if it's green.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Skyrider Patrol

Flying
At the beginning of combat on your turn, you may pay {G}{U}. When you do, put a +1/+1 counter on another target creature you control, and that creature gains flying until end of turn.

Island

Dragonsguard Elite

Magecraft — Whenever you cast or copy an instant or sorcery spell, put a +1/+1 counter on Dragonsguard Elite.
{4}{G}{G}: Double the number of +1/+1 counters on Dragonsguard Elite.

Setessan Oathsworn

Heroic — Whenever you cast a spell that targets Setessan Oathsworn, put two +1/+1 counters on Setessan Oathsworn.

Advocate of the Beast

At the beginning of your end step, put a +1/+1 counter on target Beast creature you control.

Hero of Leina Tower

Heroic — Whenever you cast a spell that targets Hero of Leina Tower, you may pay {X}. If you do, put X +1/+1 counters on Hero of Leina Tower.

Evolutionary Escalation

At the beginning of your upkeep, put three +1/+1 counters on target creature you control and three +1/+1 counters on target creature an opponent controls.

Hardened Scales

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Chronomaton

{1}, {T}: Put a +1/+1 counter on Chronomaton.

Baloth Pup

Baloth Pup has trample as long as it has a +1/+1 counter on it.

Baloth Gorger

Kicker {4} (You may pay an additional {4} as you cast this spell.)
If Baloth Gorger was kicked, it enters with three +1/+1 counters on it.

Battlegrowth

Kumena, Tyrant of Orazca

Tap another untapped Merfolk you control: Kumena, Tyrant of Orazca can't be blocked this turn.
Tap three untapped Merfolk you control: Draw a card.
Tap five untapped Merfolk you control: Put a +1/+1 counter on each Merfolk you control.

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 Durable Handicraft: Put a +1/+1 counter on each creature you control.

Gnarlid Pack

Multikicker {1}{G} (You may pay an additional {1}{G} any number of times as you cast this spell.)
Gnarlid Pack enters with a +1/+1 counter on it for each time it was kicked.

Rot Shambler

Whenever another creature you control dies, put a +1/+1 counter on Rot Shambler.

Patchwork Automaton

Ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
Whenever you cast an artifact spell, put a +1/+1 counter on Patchwork Automaton.

Deranged Outcast

{1}{G}, Sacrifice a Human: Put two +1/+1 counters on target creature.

Heroes' Bane

This creature enters with four +1/+1 counters on it.
{2}{G}{G}: Put X +1/+1 counters on this creature, where X is its power.

Glowstone Recluse

Mutate {3}{G} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.)
Reach
Whenever this creature mutates, put two +1/+1 counters on it.

Mysterious Egg

Whenever this creature mutates, put a +1/+1 counter on it.

First Responder

Vigilance
At the beginning of your end step, you may return another creature you control to its owner's hand, then put a number of +1/+1 counters equal to that creature's power on First Responder.

Chasm Skulker

Whenever you draw a card, put a +1/+1 counter on Chasm Skulker.
When Chasm Skulker dies, create X 1/1 blue Squid creature tokens with islandwalk, where X is the number of +1/+1 counters on Chasm Skulker. (They can't be blocked as long as defending player controls an Island.)

Bloodline Pretender

Changeling (This card is every creature type.)
As Bloodline Pretender enters, choose a creature type.
Whenever another creature you control of the chosen type enters, put a +1/+1 counter on Bloodline Pretender.

Biomathematician

When Biomathematician enters, create a 0/0 green and blue Fractal creature token. Put a +1/+1 counter on each Fractal you control.