Command Tower

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

Gilded Ghoda

Whenever this creature attacks while saddled, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Saddle 1 (Tap any number of other creatures you control with total power 1 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Sol Ring

Guardian Sunmare

Ward {2}
Whenever this creature attacks while saddled, search your library for a nonland permanent card with mana value 3 or less, put it onto the battlefield, then shuffle.
Saddle 4

Brightfield Mustang

Whenever this creature attacks while saddled, untap it and put a +1/+1 counter on it.
Saddle 1 (Tap any number of other creatures you control with total power 1 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)

Thurid, Mare of Destiny

Flying, lifelink
Whenever you cast a Pegasus, Unicorn, or Horse creature spell, copy it. (The copy becomes a token.)
Other Pegasi, Unicorns, and Horses you control get +1/+1.

Calamity, Galloping Inferno

Haste
Whenever Calamity 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

Lightning Mare

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

Bill the Pony

When Bill the Pony enters, create two Food tokens. (They're artifacts with "{2}, {T}, Sacrifice this token: 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.

Shield Mare

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

Plains

Mountain

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.

Arcane Signet

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.)

Shadowfax, Lord of Horses

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