Workhorse

Workhorse enters with four +1/+1 counters on it.
Remove a +1/+1 counter from Workhorse: Add {C}.

Surge Mare

Surge Mare can't be blocked by green creatures.
Whenever Surge Mare deals damage to an opponent, you may draw a card. If you do, discard a card.
{1}{U}: Surge Mare gets +2/-2 until end of turn.

Underworld Charger

Underworld Charger can't block.
Escape—{4}{B}, Exile three other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)
Underworld Charger escapes with two +1/+1 counters on it.

Thundering Mightmare

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 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."

Cosmos Charger

Flash
Flying
Foretelling cards from your hand costs {1} less and can be done on any player's turn.
Foretell {2}{U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Akroan Horse

Defender
When Akroan Horse enters, an opponent gains control of it.
At the beginning of your upkeep, each opponent creates a 1/1 white Soldier creature token.

Carnival Hellsteed

First strike, haste
Unleash (You may have this creature enter with a +1/+1 counter on it. It can't block as long as it has a +1/+1 counter on it.)

Crested Sunmare

Other Horses you control have indestructible.
At the beginning of each end step, if you gained life this turn, create a 5/5 white Horse creature token.

Universal Automaton

Changeling (This card is every creature type.)

Bill the Pony

When Bill the Pony enters, create two Food tokens. (They're artifacts with "{2}, {T}, Sacrifice this artifact: You gain 3 life.")
Sacrifice a Food: Until end of turn, target creature you control assigns combat damage equal to its toughness rather than its power.

Stallion of Ashmouth

Delirium — {1}{B}: Stallion of Ashmouth gets +1/+1 until end of turn. Activate only if there are four or more card types among cards in your graveyard.

Bill Ferny, Bree Swindler

Whenever Bill Ferny, Bree Swindler becomes blocked, choose one —
• Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
• Target opponent gains control of target Horse you control. If they do, remove Bill Ferny from combat and create three Treasure tokens.

Diamond Mare

As Diamond Mare enters, choose a color.
Whenever you cast a spell of the chosen color, you gain 1 life.

Temur Charger

Morph—Reveal a green card in your hand. (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)
When Temur Charger is turned face up, target creature gains trample until end of turn.

Realmwalker

Changeling (This card is every creature type.)
As Realmwalker enters, choose a creature type.
You may look at the top card of your library any time.
You may cast creature spells of the chosen type from the top of your library.

Fleshmad Steed

Whenever another creature dies, tap Fleshmad Steed.

Avian Changeling

Changeling (This card is every creature type.)
Flying

Shield Mare

Shield Mare can't be blocked by red creatures.
When Shield Mare enters or becomes the target of a spell or ability an opponent controls, you gain 3 life.

Tarpan

Keleth, Sunmane Familiar

Whenever a commander you control attacks, put a +1/+1 counter on it.
Partner (You can have two commanders if both have partner.)

Wavebreak Hippocamp

Whenever you cast your first spell during each opponent's turn, draw a card.

Nightmare

Flying (This creature can't be blocked except by creatures with flying or reach.)
Nightmare's power and toughness are each equal to the number of Swamps you control.

Armored Warhorse

Shadowfax, Lord of Horses

Horses you control have haste. (They can attack and {T} as soon as they come under your control.)
Whenever Shadowfax, Lord of Horses attacks, you may put a creature card with lesser power from your hand onto the battlefield tapped and attacking.

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.

Timbermare

Haste
Echo {5}{G} (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When Timbermare enters, tap all other creatures.

Phantom Steed

Flash
When Phantom Steed enters, exile another target creature you control until Phantom Steed leaves the battlefield.
Whenever Phantom Steed attacks, create a tapped and attacking token that's a copy of the exiled card, except it's an Illusion in addition to its other types. Sacrifice that token at end of combat.

Wandermare

Whenever you cast a creature spell that has an Adventure, put a +1/+1 counter on Wandermare. (It doesn't need to have gone on the adventure first.)

Zodiac Horse

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)

Taurean Mauler

Changeling (This card is every creature type.)
Whenever an opponent casts a spell, you may put a +1/+1 counter on this creature.

Mirror Entity

Changeling (This card is every creature type.)
{X}: Until end of turn, creatures you control have base power and toughness X/X and gain all creature types.

Plague Mare

Plague Mare can't be blocked by white creatures.
When Plague Mare enters, creatures your opponents control get -1/-1 until end of turn.

Vine Mare

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Vine Mare can't be blocked by black creatures.

Irregular Cohort

Changeling (This card is every creature type.)
When Irregular Cohort enters, create a 2/2 colorless Shapeshifter creature token with changeling.

Bronze Horse

Trample
As long as you control another creature, prevent all damage that would be dealt to Bronze Horse by spells that target it.

Thundermare

Haste (This creature can attack and {T} as soon as it comes under your control.)
When Thundermare enters, tap all other creatures.

Phyrexian Warhorse

Kicker {W} (You may pay an additional {W} as you cast this spell.)
When Phyrexian Warhorse enters, if it was kicked, create a 1/1 white Soldier creature token.
{1}, Sacrifice another creature: Phyrexian Warhorse gets +2/+1 until end of turn.

Dusk Charger

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
Dusk Charger gets +2/+2 as long as you have the city's blessing.

Ghoulsteed

{2}{B}, Discard two cards: Return Ghoulsteed from your graveyard to the battlefield tapped.

Adaptive Automaton

As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
Other creatures you control of the chosen type get +1/+1.

Clockwork Steed

Clockwork Steed enters with four +1/+0 counters on it.
Clockwork Steed can't be blocked by artifact creatures.
At end of combat, if Clockwork Steed attacked or blocked this combat, remove a +1/+0 counter from it.
{X}, {T}: Put up to X +1/+0 counters on Clockwork Steed. This ability can't cause the total number of +1/+0 counters on Clockwork Steed to be greater than four. Activate only during your upkeep.

Cobbled Lancer

As an additional cost to cast this spell, exile a creature card from your graveyard.
{3}{U}, Exile Cobbled Lancer from your graveyard: Draw a card.

Chrome Steed

Metalcraft — Chrome Steed gets +2/+2 as long as you control three or more artifacts.

Lightning Mare

This spell can't be countered.
Lightning Mare can't be blocked by blue creatures.
{1}{R}: Lightning Mare gets +1/+0 until end of turn.

Motivated Pony

Trample, haste
Whenever Motivated Pony attacks, attacking creatures get +1/+1 until end of turn. If a Food entered under your control this turn, untap those creatures and they get an additional +2/+2 until end of turn.