Kalonian Hydra

Trample
Kalonian Hydra enters the battlefield with four +1/+1 counters on it.
Whenever Kalonian Hydra attacks, double the number of +1/+1 counters on each creature you control.

Visions of Dominance

Put a +1/+1 counter on target creature, then double the number of +1/+1 counters on it.
Flashback {8}{G}{G}. This spell costs {X} less to cast this way, where X is the greatest mana value of a commander you own on the battlefield or in the command zone. (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Mycoloth

Devour 2 (As this enters the battlefield, you may sacrifice any number of creatures. This creature enters the battlefield with twice that many +1/+1 counters on it.)
At the beginning of your upkeep, create a 1/1 green Saproling creature token for each +1/+1 counter on Mycoloth.

Mindless Automaton

Mindless Automaton enters the battlefield with two +1/+1 counters on it.
{1}, Discard a card: Put a +1/+1 counter on Mindless Automaton.
Remove two +1/+1 counters from Mindless Automaton: Draw a card.

Ohran Frostfang

Attacking creatures you control have deathtouch.
Whenever a creature you control deals combat damage to a player, draw a card.

Steelbane Hydra

Steelbane Hydra enters the battlefield with X +1/+1 counters on it.
{2}{G}, Remove a +1/+1 counter from Steelbane Hydra: Destroy target artifact or enchantment.

Golgari Grave-Troll

Golgari Grave-Troll enters the battlefield with a +1/+1 counter on it for each creature card in your graveyard.
{1}, Remove a +1/+1 counter from Golgari Grave-Troll: Regenerate Golgari Grave-Troll.
Dredge 6 (If you would draw a card, you may mill six cards instead. If you do, return this card from your graveyard to your hand.)

The Great Henge

This spell costs {X} less to cast, where X is the greatest power among creatures you control.
{T}: Add {G}{G}. You gain 2 life.
Whenever a nontoken creature enters the battlefield under your control, put a +1/+1 counter on it and draw a card.

Ironscale Hydra

If a creature would deal combat damage to Ironscale Hydra, prevent that damage and put a +1/+1 counter on Ironscale Hydra.

Branching Evolution

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

Mold Adder

Whenever an opponent casts a blue or black spell, you may put a +1/+1 counter on Mold Adder.

Loyal Guardian

Trample
Lieutenant — At the beginning of combat on your turn, if you control your commander, put a +1/+1 counter on each creature you control.

Vinelasher Kudzu

Landfall — Whenever a land enters the battlefield under your control, put a +1/+1 counter on Vinelasher Kudzu.

Doubling Season

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.
If an effect would put one or more counters on a permanent you control, it puts twice that many of those counters on that permanent instead.

Titania's Chosen

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

Predatory Hunger

Enchant creature
Whenever an opponent casts a creature spell, put a +1/+1 counter on enchanted creature.

Invigorating Surge

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

Ochre Jelly

Trample
Ochre Jelly enters the battlefield with X +1/+1 counters on it.
Split — When Ochre Jelly dies, if it had two or more +1/+1 counters on it, create a token that's a copy of it at the beginning of the next end step. The token enters the battlefield with half that many +1/+1 counters on it, rounded down.

Algae Gharial

Shroud (This creature can't be the target of spells or abilities.)
Whenever another creature dies, you may put a +1/+1 counter on Algae Gharial.

Forgotten Ancient

Whenever a player casts a spell, you may put a +1/+1 counter on Forgotten Ancient.
At the beginning of your upkeep, you may move any number of +1/+1 counters from Forgotten Ancient onto other creatures.

Citanul Druid

Whenever an opponent casts an artifact spell, put a +1/+1 counter on Citanul Druid.

The Ozolith

Whenever a creature you control leaves the battlefield, if it had counters on it, put those counters on The Ozolith.
At the beginning of combat on your turn, if The Ozolith has counters on it, you may move all counters from The Ozolith onto target creature.

Guildmages' Forum

{T}: Add {C}.
{1}, {T}: Add one mana of any color. If that mana is spent on a multicolored creature spell, that creature enters the battlefield with an additional +1/+1 counter on it.

Thundering Mightmare

Soulbond (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them.)
As long as Thundering Mightmare is paired with another creature, each of those creatures has "Whenever an opponent casts a spell, put a +1/+1 counter on this creature."

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.

Fertilid

Fertilid enters the battlefield with two +1/+1 counters on it.
{1}{G}, Remove a +1/+1 counter from Fertilid: Target player searches their library for a basic land card, puts it onto the battlefield tapped, then shuffles.

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.

Gyre Sage

Evolve (Whenever a creature enters the battlefield under your control, 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 Gyre Sage.

Hydra's Growth

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

Paradox Zone

Paradox Zone enters the battlefield with a growth counter on it.
At the beginning of your end step, double the number of growth counters on Paradox Zone. Then create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it, where X is the number of growth counters on Paradox Zone.

Cazur, Ruthless Stalker

Partner with Ukkima, Stalking Shadow (When this creature enters the battlefield, target player may put Ukkima into their hand from their library, then shuffle.)
Whenever a creature you control deals combat damage to a player, put a +1/+1 counter on that creature.

Pheres-Band Tromper

Inspired — Whenever Pheres-Band Tromper becomes untapped, put a +1/+1 counter on it.

Primordial Hydra

Primordial Hydra enters the battlefield with X +1/+1 counters on it.
At the beginning of your upkeep, double the number of +1/+1 counters on Primordial Hydra.
Primordial Hydra has trample as long as it has ten or more +1/+1 counters on it.

Biogenic Upgrade

Distribute three +1/+1 counters among one, two, or three target creatures, then double the number of +1/+1 counters on each of those creatures.

Fractal Harness

When Fractal Harness enters the battlefield, create a 0/0 green and blue Fractal creature token. Put X +1/+1 counters on it and attach Fractal Harness to it.
Whenever equipped creature attacks, double the number of +1/+1 counters on it.
Equip {2}

Vorinclex, Monstrous Raider

Trample, haste
If you would put one or more counters on a permanent or player, put twice that many of each of those kinds of counters on that permanent or player instead.
If an opponent would put one or more counters on a permanent or player, they put half that many of each of those kinds of counters on that permanent or player instead, rounded down.

Champion of Lambholt

Creatures with power less than Champion of Lambholt's power can't block creatures you control.
Whenever another creature enters the battlefield under your control, put a +1/+1 counter on Champion of Lambholt.

Yorvo, Lord of Garenbrig

Yorvo, Lord of Garenbrig enters the battlefield with four +1/+1 counters on it.
Whenever another green creature enters the battlefield under your control, put a +1/+1 counter on Yorvo. Then if that creature's power is greater than Yorvo's power, put another +1/+1 counter on Yorvo.

Sporeback Troll

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

Biogenic Ooze

When Biogenic Ooze enters the battlefield, 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.

Hooded Hydra

Hooded Hydra enters the battlefield with X +1/+1 counters on it.
When Hooded Hydra dies, create a 1/1 green Snake creature token for each +1/+1 counter on it.
Morph {3}{G}{G}
As Hooded Hydra is turned face up, put five +1/+1 counters on it.

Scute Mob

At the beginning of your upkeep, if you control five or more lands, put four +1/+1 counters on Scute Mob.

Beast Whisperer

Whenever you cast a creature spell, draw a card.

Wildwood Scourge

Wildwood Scourge enters the battlefield with X +1/+1 counters on it.
Whenever one or more +1/+1 counters are put on another non-Hydra creature you control, put a +1/+1 counter on Wildwood Scourge.

Oran-Rief Ooze

When Oran-Rief Ooze enters the battlefield, put a +1/+1 counter on target creature you control.
Whenever Oran-Rief Ooze attacks, put a +1/+1 counter on each attacking creature with a +1/+1 counter on it.

Vigor

Trample
If damage would be dealt to another creature you control, prevent that damage. Put a +1/+1 counter on that creature for each 1 damage prevented this way.
When Vigor is put into a graveyard from anywhere, shuffle it into its owner's library.

Managorger Hydra

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

Dirtcowl Wurm

Whenever an opponent plays a land, put a +1/+1 counter on Dirtcowl Wurm.

Slurrk, All-Ingesting

Slurrk, All-Ingesting enters the battlefield with five +1/+1 counters on it.
Whenever Slurrk or another creature you control dies, if it had a +1/+1 counter on it, put a +1/+1 counter on each creature you control that has a +1/+1 counter on it.
Partner (You can have two commanders if both have partner.)

Primal Vigor

If one or more tokens would be created, twice that many of those tokens are created instead.
If one or more +1/+1 counters would be put on a creature, twice that many +1/+1 counters are put on that creature instead.

Gutter Grime

Whenever a nontoken creature you control dies, put a slime counter on Gutter Grime, then create a green Ooze creature token with "This creature's power and toughness are each equal to the number of slime counters on Gutter Grime."

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.

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.

Forest

Toski, Bearer of Secrets

This spell can't be countered.
Indestructible
Toski, Bearer of Secrets attacks each combat if able.
Whenever a creature you control deals combat damage to a player, draw a card.

Experiment One

Evolve (Whenever a creature enters the battlefield under your control, 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, instead tap it, remove it from combat, and heal all damage on it.)

Fangren Firstborn

Whenever Fangren Firstborn attacks, put a +1/+1 counter on each attacking creature.

Predator Ooze

Indestructible
Whenever Predator Ooze attacks, put a +1/+1 counter on it.
Whenever a creature dealt damage by Predator Ooze this turn dies, put a +1/+1 counter on Predator Ooze.

Heroes' Bane

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