Calamity, Galloping Inferno

Haste
Whenever Calamity, Galloping Inferno attacks while saddled, choose a nonlegendary creature that saddled it this turn and create a tapped and attacking token that's a copy of it. Sacrifice that token at the beginning of the next end step. Repeat this process once.
Saddle 1

Zhang Fei, Fierce Warrior

Vigilance; horsemanship (This creature can't be blocked except by creatures with horsemanship.)

Guan Yu, Sainted Warrior

Horsemanship (This creature can't be blocked except by creatures with horsemanship.)
When Guan Yu, Sainted Warrior is put into your graveyard from the battlefield, you may shuffle Guan Yu into your library.

Zhao Zilong, Tiger General

Horsemanship (This creature can't be blocked except by creatures with horsemanship.)
Whenever Zhao Zilong, Tiger General blocks, it gets +1/+1 until end of turn.

Workhorse

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

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.

Chrome Steed

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

Ma Chao, Western Warrior

Horsemanship (This creature can't be blocked except by creatures with horsemanship.)
Whenever Ma Chao, Western Warrior attacks alone, it can't be blocked this combat.

Yuan Shao, the Indecisive

Horsemanship (This creature can't be blocked except by creatures with horsemanship.)
Each creature you control can't be blocked by more than one creature.

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.)

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.

Diamond Mare

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

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.

Yellow Scarves Cavalry

Horsemanship (This creature can't be blocked except by creatures with horsemanship.)
Yellow Scarves Cavalry can't block.

The Spear of Leonidas

Whenever equipped creature attacks, choose one —
• Bull Rush — It gains double strike until end of turn.
• Summon — Create Phobos, a legendary 3/2 red Horse creature token.
• Revelation — Discard two cards, then draw two cards.
Equip {2}

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.

Thundermare

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

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.

Lu Bu, Master-at-Arms

Haste; horsemanship (This creature can't be blocked except by creatures with horsemanship.)

Trenching Steed

Sacrifice a land: Trenching Steed gets +0/+3 until end of turn.

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.

Shu General

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.